Prepare the vegetable stock. Add 1 onion, 2 carrots, and 2 celery hearts to a pan of boiling water, and let it simmer for 30 minutes. Add a handful of coarse salt.
Meanwhile, cut the remaining onion finely. Warm the oil, add the onion to the pan, and cook for a few minutes.
Add the rice and toast it. The rice has to become translucent.
Blend with Prosecco.
Once the liquid has been absorbed, start adding the stock gradually, stirring all the time.
The rice needs to cook for about 20 minutes. It is ready when it has become soft.
Once the rice is cooked, add the mascarpone, Parmesan cheese, and half of the peppercorn. Let it rest for 5 minutes.
Plate the rice.
Garnish with the remaining peppercorn and the gold leaf.
Serve it hot.