Crab and Broccoli Gratin with Roasted Red Pepper

A gratin gets its name from the crust — from the French word gratter, to scrape — and the best part of any gratin is exactly that: the bubbled, browned top that you drag your spoon through on the way to the creamy layer underneath. Crab and broccoli gratin with roasted red pepper earns that crust properly. The roasted red pepper works into the béchamel and gives it a sweet, smoky depth that plain cream sauce cannot approach on its own. The broccoli holds its structure through the oven time. The crab — sweet, delicate, already cooked — goes in last and barely needs the heat at all.

This is a dish that works for a weeknight if you move efficiently, and it works even better for a small dinner party because most of it can be assembled hours ahead. It comes out of the oven looking and smelling like you put in significantly more effort than you did.

Why Crab and Broccoli Gratin with Roasted Red Pepper Belongs in Your Rotation

Gratins have a reputation for being heavy, and a lot of them are. This one avoids that trap because the broccoli and crab are the main event, not fillers floating in a cheese sauce. The sauce is there to bind and season, not to be the whole dish. You get something that is rich without being dense — a meaningful distinction when you actually sit down to eat it.

The roasted red pepper is the move that makes this recipe specific. It takes what would otherwise be a fairly standard crab bake and gives it a flavor signature that holds up in every bite. The sweetness of the pepper mirrors the sweetness of the crab. The smokiness — especially if you char the peppers yourself rather than using jarred — gives the whole dish a subtle depth that keeps it interesting across the full serving.

Assembly takes about 20 minutes once your pepper is roasted and your broccoli is blanched, and then the oven does the rest. It is genuinely weeknight-viable if you roast the pepper a day ahead, and genuinely impressive if you serve it to guests.

What You’ll Need

All quantities are for 4 servings in a 2-quart (roughly 23x33cm) baking dish. The sauce and vegetables can be assembled up to 6 hours ahead; add the crab just before baking.

For the Gratin

• 340g (12 oz) cooked crab meat — lump or claw, picked over for shells. Fresh is best; good-quality refrigerated pasteurized crab is a solid substitute. Canned crab works but has a noticeably softer texture and more pronounced briny flavor. Drain it thoroughly and press it dry with paper towels regardless of which you use.
• 1 large head broccoli (about 500g), cut into small florets — no larger than 4cm across. Larger pieces hold too much water and make the gratin wet at the bottom.
• 2 large red bell peppers — to be roasted and peeled. Jarred roasted red peppers (drained and patted dry) can substitute; you lose some of the char character but the sweetness is still there.
• 3 tablespoons unsalted butter
• 3 tablespoons all-purpose flour — the roux base for the béchamel.
• 2 cups (480ml) whole milk, warmed — cold milk added to a hot roux creates lumps that are difficult to smooth out. Warm it in the microwave for 90 seconds before it goes in.
• 1/2 cup (50g) grated Gruyère — melts cleanly into the sauce and provides a nutty, slightly earthy note. Sharp cheddar works and gives a more assertive flavor; fontina gives a creamier, milder result.
• 1/3 cup (35g) grated Parmesan — split: half goes into the sauce, half goes on top for the crust.
• 1 tablespoon Dijon mustard — stirs into the sauce and sharpens it without being detectable as mustard. Do not skip it.
• 1/4 teaspoon freshly grated nutmeg — a classic béchamel addition that adds warmth; pre-ground works but is less potent.
• Salt, white pepper, and cayenne to taste

For the Topping

• 1/3 cup (35g) panko breadcrumbs — combined with the reserved Parmesan for the top crust. Panko produces a lighter, crisper topping than regular breadcrumbs.
• 1 tablespoon melted butter — tossed with the panko before sprinkling.

How to Make It

1. Roast the red peppers. Place the whole peppers directly over a gas flame or under a broiler, turning with tongs every few minutes, until the skin is charred and blistered on all sides — 10–15 minutes total. Transfer to a bowl, cover tightly with plastic wrap or a plate, and let steam for 15 minutes. The steam loosens the skin for easy removal. Peel off the charred skin, remove the seeds and stem, and chop the flesh into roughly 1cm pieces. Set aside. If the peppers release a lot of liquid, blot them with a paper towel — excess moisture goes into your sauce and thins it.
2. Blanch the broccoli. Bring a large pot of salted water to a boil. Add the broccoli florets and cook for exactly 3 minutes — just enough to take the raw edge off while keeping them firm enough to hold up in the oven. Drain and immediately transfer to a bowl of ice water to stop the cooking. Once cold, drain again and spread on a clean kitchen towel. Pat thoroughly dry. Wet broccoli is the primary cause of a watery gratin.
3. Make the béchamel. Melt the butter in a medium saucepan over medium heat. Once it foams and the foam subsides, add the flour and stir constantly for 2 minutes. You are cooking out the raw flour taste — the mixture (called a roux) should smell faintly nutty and look pale gold. Add the warm milk in a slow, steady stream while whisking continuously. Keep whisking as the sauce thickens, about 4–5 minutes, until it coats the back of a spoon thickly enough that a line drawn through it holds its shape. Remove from heat. Stir in the Gruyère, half the Parmesan, the Dijon mustard, nutmeg, and a generous pinch each of salt, white pepper, and cayenne. Taste and adjust — the sauce should be noticeably well-seasoned since it will tone down when combined with the other components.
4. Fold in the peppers. Add the chopped roasted red peppers to the warm béchamel and stir to combine. The sauce will turn a pale terracotta-orange. At this point you can let it cool and refrigerate it for up to 6 hours if you are prepping ahead.
5. Assemble the gratin. Heat your oven to 190°C (375°F). Lightly butter your baking dish. Arrange the dried broccoli florets in an even layer across the bottom. Scatter the crab meat over the broccoli, distributing it as evenly as you can without pressing it down — you want it to stay in distinct pieces, not become a uniform layer. Pour the roasted red pepper béchamel evenly over the top, nudging it into the gaps with a spoon.
6. Add the topping. Toss the panko with the melted butter until the crumbs are evenly coated. Mix in the reserved Parmesan. Scatter this mixture in an even layer across the surface of the gratin — it should cover the sauce fully but not be piled thick.
7. Bake. Place the gratin on the middle rack and bake for 22–25 minutes, until the sauce is bubbling at the edges and the top is deeply golden. If the crust is browning too quickly before the sauce bubbles, tent loosely with foil and remove it for the last 5 minutes. The gratin is done when it bubbles actively around the perimeter — not just at one edge, but all the way around. Let it rest for 5 minutes before serving; the sauce will tighten slightly and portions will hold their shape better.

Tips That Actually Make a Difference

Dry everything aggressively. This is the single most important thing you can do for this gratin. Wet broccoli, undrained crab, and wet roasted peppers all release moisture in the oven and pool at the bottom of the dish. The result is a watery gratin with a soggy underside instead of the creamy, cohesive texture you are after. After blanching the broccoli, give it at least 5 minutes on a towel. After draining the crab, press it between paper towels. After peeling the peppers, blot them before chopping.

Season the béchamel more than feels right. The sauce is going to be diluted when it coats the broccoli and crab, and it will lose perceived saltiness as it cools slightly in the oven. A sauce that seems properly seasoned on the stovetop will taste underseasoned in the finished gratin. Add the salt and white pepper, taste, then add a little more.

Use a shallow baking dish rather than a deep one. Shallower depth means more surface area for the topping and better heat distribution through the layers. A deep dish insulates the center and can leave the broccoli undercooked in the middle while the edges are done.

The five-minute rest after baking is real. A gratin pulled straight from the oven and immediately portioned will flow across the plate. Five minutes of resting lets the béchamel re-set enough to serve cleanly. It also protects your guests from burning their mouths, which is worth mentioning.

Mistakes to Watch Out For

Adding cold milk to the roux. Cold milk hits the hot roux unevenly and creates lumps that require aggressive whisking to smooth out — and sometimes they never fully smooth out. Warm your milk before it goes in. If you end up with lumps anyway, pass the finished sauce through a fine-mesh sieve before adding the cheese.

Do not overbake. Once the crab and broccoli gratin with roasted red pepper is bubbling and golden, it is done. Extending the bake time to get a darker crust dries out the crab and turns the broccoli mushy. The crab is already cooked — it only needs to heat through in the sauce, not cook further. If you want a darker top without extra oven time, hit it with the broiler for 90 seconds at the very end.

Skipping the blanching step. Raw broccoli in a 35-minute gratin will be simultaneously overcooked at the floret tips and undercooked near the stem. The 3-minute blanch gives you a head start so everything finishes at the same time in the oven. The ice bath is equally important — without it, the broccoli continues cooking from residual heat and goes mushy before it even reaches the oven.

Using imitation crab. It is not a workable substitute here. Imitation crab releases a significant amount of water when heated, which dilutes the sauce, and its texture becomes rubbery under the heat of the gratin. Spend the money on real crab, even if it means buying the more affordable claw meat instead of lump.

Easy Ways to Change It Up

Swap crab for cooked shrimp — cut into bite-sized pieces if large, left whole if small. The flavor profile shifts but the technique is identical. Add the shrimp raw if they are very small; they will cook through in the oven. Larger shrimp should be briefly sautéed first or they can become rubbery by the time the gratin is done.

Add a layer of thinly sliced leek softened in butter before it goes under the broccoli. Leek and crab have a quiet affinity — the leek’s mild sweetness amplifies the crab rather than competing with it, and it adds another textural layer to the dish.

Replace the Gruyère with smoked Gouda for a version where the smokiness is more pronounced. This works particularly well if you are using jarred roasted red peppers, which have less char character — the smoked Gouda compensates for what the peppers are missing.

Make it gluten-free by swapping the all-purpose flour for a 1:1 gluten-free flour blend in the roux and using gluten-free panko for the topping. The sauce will be slightly less cohesive but perfectly serviceable.

What to Serve It With

Crab and broccoli gratin with roasted red pepper is rich enough to anchor a meal without much support. A simple green salad dressed with something acidic — lemon vinaigrette, a sharp red wine vinaigrette — works well alongside because the acidity cuts through the sauce in a way that a starchy side cannot. Arugula with shaved fennel and lemon is a particularly good match.

If you want something more substantial, serve it over or alongside lightly buttered egg noodles — the sauce coats them beautifully where it spills over during portioning. Crusty bread to scrape the dish is also not optional in my house, for whatever that’s worth.

For a dinner party, this gratin works as a main alongside a simple roasted asparagus or a warm grain salad. It does not need another rich element on the table — keep the accompaniments light and let the gratin be the centerpiece it is.

Leftovers and Reheating

Store leftover gratin covered tightly in the refrigerator for up to 2 days. The topping will soften overnight as it absorbs moisture from the sauce — this is unavoidable. The flavor actually improves slightly as everything continues to meld, but the textural contrast between crust and filling is reduced.

To reheat, cover the dish with foil and warm in a 175°C (350°F) oven for 15–18 minutes until heated through. Remove the foil for the last 3–4 minutes to re-crisp the topping as much as possible. The microwave reheats it faster but turns the panko soft and the broccoli limp — use it only if oven reheating is not practical, and cover the dish with a damp paper towel to prevent the crab from drying out.

Leftovers also work well stirred into cooked pasta with a splash of milk to loosen the sauce — a repurposing that uses every bit of the dish without feeling like leftovers at all.

Approximate Nutrition Per Serving

These are estimates for informational purposes only, calculated for 4 equal servings. Values will vary based on crab type, cheese brands, and exact quantities used.

The thing that makes crab and broccoli gratin with roasted red pepper worth coming back to is not any single component — it is how well they all read together. The roasted red pepper béchamel does something that a plain cream sauce never quite does, and once you have tasted it you will find yourself using that same roasted-pepper idea in other sauces. That transferable quality is what separates a good recipe from a useful one.

Pick up some crab this week and give it a go — it is the kind of dish that earns its spot at the table.