Cover with hot water for 20 minutes. Strain and save the soaking liquid.
In a pot, cook onion in 1 tbsp butter until soft. Add chopped porcini.
Stir in the rice and toast for 1 minnute.
Pour in wine and cook until evaporated
Add hot broth and soaking liquid, one ladle at the time, stirring unitl absorbed before adding more. Repeat until rice is creamy and al dente.
Turn off heat. Stir in remaining butter and Parmesan. Mix well and serve.