Put the milk in a saucepan on the stove, add a knob of butter, a large pinch of salt and the nutmeg; as soon as the milk boils, pour in the Molino Riva semolina, stirring vigorously with a whisk to prevent lumps from forming. Cook the mixture over low heat for a few minutes, till the semolina thickens, then remove the pan from the stove and add the two yolks and 80 grams of grated Parmesan cheese to the mixture. Oil a large baking tray with low edges and pour the mixture, levelling it with the help of a wet knife to make a layer of about 1 cm. Take a baking dish and butter it. Turn on the oven at 200°. As soon as the semolina has cooled down, with the help of a round cutter or a glass, cut many discs with a diameter of about 5 cm, place them in the baking dish, slightly overlapping one disc on the other. When you have placed all the discs in the baking dish, sprinkle the surface with grated Parmesan and Gruyere cheese. Melt the remaining butter and sprinkle the preparation well. Place the dish in the preheated oven and leave your Gnocchi alla Romana au gratin for about 20-25 minutes, until a nice golden crust forms.
