Line a sieve with a piece of muslin or a new J-cloth and place over a bowl. Tip the ricotta into the cloth, gently gather up the ends and secure with an elastic band. Leave the ricotta to drain for 4 hrs.
Transfer the drained ricotta to a clean bowl. Beat in the hard cheese, egg yolk, a good grating of nutmeg, then season well. Tip the semolina into a baking dish or large plastic container. Wet your hands, dip them in the semolina and, working quickly, scoop 1 heaped tsp of the ricotta mix into your hands and gently roll into a ball (don’t worry if it’s not perfect). Place the ball in the semolina dish and roll around so that it is totally covered. Pick it up and roll between the palms of your hands to create a smooth ball, then pop back into the semolina. Continue with the rest of the mixture. You should make about 24 balls. Once all the balls are formed and are sitting in the semolina, cover loosely with baking parchment (not cling film), put the dish in the fridge and leave to chill for at least 12 hrs, although
24 hrs is better – this is so the balls of ricotta form a skin around the outside.
When ready to serve, bring a large pan of salted water to the boil. Turn down to a simmer and lower in half the gnudi. Cook gently for 2-3 mins – they’re ready when they float to the top – then scoop out with a slotted spoon and transfer to a sieve. Repeat with the remaining gnudi. Slowly melt the butter in a small frying pan. Add the sage leaves, making sure they don’t overlap, and let them sizzle until crisp. Transfer to a plate lined with kitchen paper. If the butter has turned a nutty brown, remove from the heat; if not, continue to bubble until lightly browned. Divide the gnudi between warmed plates, drizzle over the browned butter, top with the sage and pine nuts, and serve with grated cheese, black pepper and a rocket & red onion salad.