For the chestnut casserole, cut the chestnuts, put them in the oven until they crack and peel them. Cook the chestnuts in the milk until they break down.
Pass through a sieve or puree with a blender. Cream the mixture with butter, egg yolk and sugar. Add the mascarino liqueur and stiff egg whites.
Butter a baking dish and bake the maronia casserole in the preheated oven for 45 minutes.