For preparing the fennel:
For the béchamel sauce:
Trim the fennel and cut each bulb into into quarters (or six segments if the bulbs are large) slicing them lengthways from top to bottom. Don’t throw away the leafy green fronds. Keep them for the decoration.
In the meantime bring a large pot of salted water to the boil. Add the fennel chunks and simmer uncovered for 5-6 minutes. Next gently take the fennel pieces out of the pan and place them in a colander (in order to get rid of excess water) and allow them to cool down a little.
In a large pan melt the butter and fry the fennel chunks on both sides until they turn lightly golden in colour.
Heat the oven to 200 C.
Now prepare the sauce.
Melt the butter in a pan, stir in the flour and cook over a medium heat for a couple of minutes. Gradually (very important, otherwise you risk having lumps) whisk in the milk until it is incorporated and keep stirring whilst you bring the sauce to the boil. Continue stirring for a couple of minutes until thickened. Season with some salt and nutmeg and taste again.
Spread the fennel neatly in a baking dish and pour over the béchamel sauce.
Sprinkle the dish with grated parmesan and bake in the preheated oven to 200 C for about 20 minutes until golden brown and bubbling.
Decorate the gratin with torn green fennel fronds. Serve straight from the oven as a side dish or with a green salad and some crusty bread.