Stir the flour, eggs, milk, and a pinch of salt into a smooth mixture. The mixture should be enough to produce 10 crêpes.
Melt butter in a pan before frying the bacon. Add the diced onion and spinach, frying the ingredients until the spinach has wilted.
Melt butter in a pot. Add the flour and keep stirring the mix so that no lumps form. Pour in the milk and season with salt, pepper, and nutmeg.
Spoon a generous helping of spinach and bacon onto the crêpe and spread it out. After sprinkling on some mozzarella, spread three tablespoons of béchamel sauce on top before adding the next crêpe. Keep on building your cake like this until all the crêpes are used up: spinach, cheese, béchamel sauce. To finish, spread some tomato sauce, mozzarella, and béchamel sauce on the uppermost crêpe. Bake the cake at 355°F for 15 minutes.