To prepare the cream sauce: put 40 grams of the melted butter in a saucepan, pour in the flour, add the milk and mix to avoid lumps forming, adding a bit of nutmeg and salt.
To prepare the fennels au gratin: clean the fennels by cutting the tops and the outside leaves, divide them into quarters and immerse them in boiling salted water.
After 10 minutes, drain the fennels and gild them in a buttered pan for another 10 minutes. Once golden, lay them in a casserole dish, pour the cream sauce over the top and sprinkle them with Genovese cheese for pasta.
Now is the time to put them in the oven: after 20-25 minutes at 200°, when a beautiful golden crust has formed, take the fennels out of the oven, allow them to cool and serve.