Toast the hazelnuts by putting them in a small dry frying pan and cooking them at a moderate temperature on the stove-top for 5 minutes.  Let cool, then chop roughly.

Heat the stock in a pot on the stove until it is simmering.

While the stock is heating, finely chop the onion.

Heat 4 Tbsp of olive oil in a different large, heavy-based pot.  Saute the onion until it becomes translucent.

Add the rice and stir until it browns slightly.

Add the prosecco and let it boil off.

Pour in enough heated stock to cover the rice mixture. and put the timer on for 13 minutes.

Add  the salt and stir in.

As the rice is cooking, watch the level of the water.  As it goes down, add water from the simmering pot, one ladle-full (or cupful) at a time. Stir the rice often.

As the time gets to around 12 minutes, start tasting the rice to see how done it is. The type of rice you have may vary the cooking times. If it's close to being cooked, don't add any more water and let the water in the rice boil off, stirring frequently.

Just before you take the risotto off the heat, add the Parmesan cheese and stir it in.

Sprinkle the risotto with the chopped hazelnuts before serving.