Prep. time: 40 minutes
Cooking time: 15 minutes

 (1) The "oignons pays" (scallions) can be replaced by green onions.

1.  Halve the plantains widthwise and boil in salted water for 5 minutes; they should be firm but tender.
2. Sauté the finely chopped onion and scallion in butter until lightly colored; season with salt and pepper. Sprinkle in the flour and stir to form a roux.
3. Off the heat, gradually whisk in the milk. Stirring constantly, bring to a boil until the sauce thickens. Mix in half the grated cheese at the end. 
4. Butter a baking dish, spread a layer of sauce, cover with a layer of plantain that you have sliced into rounds, and continue layering to fill the dish, finishing with the sauce.
5. Sprinkle with the remaining cheese and brown in the oven.