Set the Instant Pot to Sauté and let it heat 2 full minutes before adding anything, until a drop of water sizzles and evaporates almost instantly.
Add the butter for the plantains. Once melted and foaming, add the plantain slices in a single, uncrowded layer, working in two batches if needed.
Sprinkle with brown sugar and cinnamon. Cook undisturbed 3 to 4 minutes, until deep golden brown, then flip and cook 2 to 3 minutes more, until glossy. Remove.
Wipe the pot. Return to Sauté and add the prosciutto in a single layer, without added fat.
Cook 1 to 2 minutes, until the edges curl and the meat crackles when moved with tongs. Remove immediately.
Wipe the pot again. Add the remaining butter, then toast the bread 1 to 2 minutes per side, until golden and crisp.
Spread each slice with ricotta, top with plantains and prosciutto, and finish with honey and chili flakes if using.