Put the semolina in a pan, add less than a spoon of salt, milk and mix it with a whisk. Cook in the steam oven at 100°C for 10 minutes, take out of the oven and add 20 g of butter, half of the cheese, the egg, pepper and grated nutmeg.
Place the dough on a smooth surface. Give it a rectangular shape and make it 1,5-2 cm tall. Let the dough cool for at least 10-15 minutes, then cut out circles by using pastry rings or a glass with a diameter of more or less 6 cm, dipping it every time in cold water.
Place the gnocchi on a buttered tray by slightly overlapping them. Melt the leftover butter with sage leaves and pour it over the gnocchi, then cover them with the grated cheese left. Bake in the already hot oven at 180-200°C for more or less 30 minutes