Soak the dried porcini in 250 ml hot water for 20 minutes. Drain, reserving the soaking liquid. Chop the porcini and strain the liquid through a fine sieve; add to the warm stock.
Heat 2 tbsp olive oil and half the butter in a large wide pan. Sauté the fresh mushrooms over high heat until golden. Season and set aside.
In the same pan, heat the remaining oil over medium heat. Sauté the onion until softened, about 5 minutes. Add the garlic and cook 1 minute more.
Add the rice and stir to coat in the oil. Toast for 2 minutes.
Pour in the white wine and stir until absorbed.
Add the warm stock one ladleful at a time, stirring frequently and waiting until each addition is absorbed before adding the next. Continue for 18–20 minutes until the rice is creamy and al dente.
Stir in the sautéed mushrooms and chopped porcini. Remove from heat.
Stir in the remaining butter and Parmigiano-Reggiano. Season to taste. Rest for 2 minutes, then serve garnished with parsley.
