In a heavy pan, melt the butter, add the onion and cook for a few minutes. Add the half of the white wine and let the alcohol evaporate, so only the acidic part remains. Filter everything through a sieve to eliminate the rest of the onion, then add the butter in pomade.
This is the procedure for making sour butter that will be used to stir in the risotto at the end.
In another pot, toast Carnaroli rice in a bit of butter for a few minutes. Wet with wine, let it evaporate. Pour a light broth over it and add the saffron threads. Cook for around 18 minutes. Once done, mix with parmigiano cheese and the soured butter prepared in advance.
Spread rice on plates and arrange on each a leaf of edible gold.