2) Put the potato in a large bowl with the salt, nutmeg, baking powder, 110g of the grated Parmesan and the egg white. Add the flour a little at a time and mix with your hands until the mixture forms a rough dough. Do not over-work the dough.
3) Transfer the dough to a lightly floured surface. Gently knead the dough for 1 or 2 minutes until smooth, adding a little bit more flour, if necessary, to keep it from sticking.
4) Break off a piece of dough and roll it back and forth into a rope, about the thickness of your index finger. Cut the rope into 2.5cm pieces. Gently roll each piece down the prongs of a fork while pressing a small dimple with your finger in the back. The gnocchi should be slightly curved and marked with ridges so it will hold the sauce when served. Make all the gnocchi and then cover with plastic wrap and refrigerate for up to 12 hours.
5) Boil the gnocchi in batches in plenty of salted water. They are done about 2 minutes after they float to the surface. Remove with a slotted spoon and reserve about 120ml of the cooking water. If not cooking immediately, place the gnocchi in a single layer on a baking pan dusted with flour.
Note: If the gnocchi start to feather and fall apart in boiling water, you need more flour. If the gnocchi don't float after 2 minutes and are hard, you used too much flour.
6) Meanwhile, preheat the oven to 180C/Gas 4 again. Blanch the peas in hot water, drain and set aside. Place the prosciutto on a baking tray and place in the oven. Cook until the bacon is crispy, 8 to 10 minutes.
7) Add the chopped shallots to a frying pan over a medium high heat with 2 tbsp of olive oil and gently saute until fragrant and translucent. Add the drained peas and toss gently to coat. Season with a little salt and pepper.
8) Add the boiled gnocchi to the pan and gently toss. Add a ladle of gnocchi water to the pan, add the butter, sprinkle with Parmesan and season with salt and pepper. Serve the gnocchi topped with crispy prosciutto and a scoop of fresh lemon ricotta. Finish with a drizzle of white truffle oil, if desired.
For the lemon ricotta:
1) Place the ricotta cheese in a mixing bowl and add the lemon zest and juice.
2) Mix well, season with salt and serve with the gnocchi.