Fish in creamy sauce

1. 1 Season the fish fillets with lime, salt, pepper and garlic.
2. 2 Roll the fillets like a roulade and place them in a Pyrex dish with olive oil and crushed garlic at the bottom. After arranging the fillets, drizzle with olive oil and bake in a hot oven for about 15 minutes.
3. 3 Remove from the oven, cover with the béchamel sauce and grated cheese, and return to the oven until the top is golden and bubbly (gratin).

Béchamel sauce

1. 4 In a pot, put 50 gr of butter or margarine and 1 tablespoon of grated onion. Cook over heat, stirring constantly, until the onion cooks without changing color (this is important).
2. 5 Add 1 tablespoon of flour and stir quickly, continuing to stir until the flour starts to change color, without darkening.
3. 6 Gradually add 1 glass of warm milk, stirring constantly until it reaches the consistency of thick porridge.