Wash the chicory, cut off a small piece from the bottom, and steam them until cooked in a steam oven or steamer.
Let cool and squeeze out all the moisture from the chicory. It's important to avoid having a watery sauce.
Roll each head of chicory in a slice of ham and arrange in a baking dish.
Steam the potatoes, mash them with the butter, egg, season, and let cool for a moment.
For the béchamel sauce, melt the butter in a large pot, once it foams, add the flour all at once and sauté briefly, add a large splash of milk and whisk until you have a thick smooth sauce, add the rest of the milk and season.
Set aside some of the cheese.
Stir the cheese well into the sauce and pour over the ham.
Finish with the remaining cheese.
Stir the mashed potatoes again and fill a piping bag with a large star nozzle and place in a preheated oven at 190°C for 30 minutes.
If you don't have a piping bag, you can also just place dollops or quenelles along the edge.
Hands up for those who fight for the cheese edges of the dish, guilty!