Unwrap the cauliflower in bunches, wash it well and boil it in salted water for about 15 minutes. When it is boiled, we put it in a strainer and pass it under a stream of cold water. We let it drain.
Put the butter in a saucepan and when it heats up, add the flour, stirring quickly for homogenization. Thin with milk, season with salt and pepper and simmer for a few minutes until the composition thickens like sour cream. Take the pan off the heat, let it cool and add the yolks and grated cheese. Lightly incorporate the beaten egg whites with a pinch of salt.
Grease a heat-resistant dish (size 18 cm in diameter) with butter, place the cauliflower and pour the sauce. Shake the bowl lightly so that the sauce is evenly distributed and covers all the cauliflower. Put it in the preheated oven over medium heat for 45-50 minutes, until it browns nicely.