Whisk the flour with milk, butter and a pinch of salt. Stir in eggs. Pour the dough through a sieve and let it rest for 10 minutes.
In the meantime, squeeze out the spinach and roughly chop it. Mix the ricotta, mascarpone, spinach, yolk and 1 tablespoon parmesan, season well with salt, pepper and grated nutmeg.
Preheat the oven to 220 °. Grease a baking dish with butter.
Bake 6 thin pancakes one after the other in a little oil. Brush the pancakes with filling, fold in 2-3 cm on both sides and roll up. Cut the rolls into 4 parts each and place them in the mold with the cut surface facing upwards. Sprinkle the rolls with the rest of the parmesan, cover with a few flakes of butter and bake in the preheated oven for about 10 minutes.