Mix the first six ingredients together with a fork, then shape in small balls by rolling in hand.
Roll the balls in semolina, they place uncovered on a tray in the fridge for at least 7-8 hours to form a skin.
Boil them in salted water until they have risen to the top.
For the Sage-Butter Sauce: melt some butter in a pan with sage leaves. Add parmigiano and salt, stirring until thickened.
Place the gnudi in the sauce, spooning the sauce over them, and serve.
