Preheat the oven to 200 C (400 F)

Prepare the bechamel sauce melting the butter over low heat. Add the onion and cook until transparent. Then add the flour and integrate well. Pour the milk, the nutmeg and a pinch of salt and black pepper. Stir incessantly until thick. (note 1)

Cook the broccoli for 3 minutes in boiling water. The broccoli must stay crunchy.

Place the broccoli in an oven casserole. Cover with bechamel sauce, mozzarella, and top with parmesan.

Cook in the oven for 10 minutes.