Prepare the crepes:
In a bowl, mix the eggs with the milk, then add the sifted flour and a pinch of salt, stirring with a whisk to obtain a smooth batter, leave to stand for about 30 minutes.
Cook the crepes in a non-stick pan greased with a little butter, pouring in one ladle of batter at a time. Cook each crepe for about 1 minute per side, then set aside.
Stuff the crepes:
Roll out a crepe on the work surface, stuff it with a slice of cooked ham, a few cubes of mozzarella and a sprinkling of Grana Padano PDO.
Roll the crepe, or fold it in half, and place it in a lightly buttered baking dish. Repeat with all the crepes.
Prepare the gratin:
Pour the béchamel sauce over the crepes arranged in the baking dish, spreading it evenly to cover them.
Finish with a generous sprinkling of Grana Padano PDO and a few knobs of butter.
Bake in the oven:
Bake at 180°C in a static oven (160°C if ventilated) for about 20-25 minutes, until the surface is nicely gratinated and golden brown.
Remove from the oven and leave to cool slightly before serving.