Put the ricotta, Parmesan and nutmeg into a bowl and beat together until smooth.
Pour the semolina into a shallow tray. Slightly wet the palms of your hands and briefly lay them in the semolina. Now take up a small piece of the ricotta mix [a large teaspoon, say], gently roll it into a ball about the size of a big marble and drop it into the semolina. Push the tray back and forth to fully coat the ball with semolina and continue this process until all the ricotta mixture is used up. Transfer the gnudi into a tub, sprinkle semolina between each layer and on top, making sure the dumplings are well covered.
Place in the fridge, covered, overnight.
The next day, carefully lift out the gnudi from the semolina and put onto a large plate lined with kitchen paper.
Put a large, wide pot of lightly salted water on to boil [also, have four hot plates ready to hand].
Meanwhile, melt the butter over a low heat. When it is frothing, toss in the sage leaves, gently cook them until crisp, and without the butter becoming too brown; it should, however, smell nutty and look golden. Once the leaves are crisp, lift them out and set them to one side, turn off the heat but leave the sage infused butter in the pan.
Once the water boils, turn it down to a simmer and slide in the gnudi. Now turn up the heat a touch and patiently wait until the gnudi float to the surface; about 4-5 minutes.
When all the gnudi have risen, carefully lift them out [they are delicate] using a slotted spoon, draining them well, and divide equally between four hot plates.
Turn the heat up under the melted butter to warm it back up. Sprinkle the sage leaves over the gnudi.
Spoon over the warm butter and serve without delay. Hand extra parmesan at table for those who want it: Me.