Peel the onions and chop finely, then pour into a pan to fry with 20 g of butter.
When the onions are golden, add the rice and let it roast for 4 minutes under low heat.
Pour the white wine and let the alcohol vapor evaporate.
Add a ladle of broth a little at a time until the rice is perfectly cooked.
Remove from heat. Stir in butter and grated Parmesan cheese, and let it rest for a few minutes.
Garnish with a few slices of red onion and serve hot.