Preheat the oven to 375°F (190°C).
Melt the butter, add the leek, and cook 3 to 4 minutes until softened.
Add the cabbage and cook 5 to 6 minutes until it begins to wilt. Stir in the corn.
Pour in the cream, season with salt and pepper, and stir. Cover and bake.
Bake 25 to 30 minutes, until the cabbage is tender and the sauce has thickened.
Stir in the Gruyère and chives. Keep warm.
Pat the scallops very dry and season both sides with salt and pepper.
Heat the oil in a separate skillet over high heat. Add the butter, then the scallops in a single layer.
Sear 2 to 3 minutes per side, until golden and just opaque throughout.
Arrange the scallops on top of the cabbage casserole and serve immediately.