In a large skillet, heat 1 tablespoon butter and olive oil over medium heat.
Add mushrooms and cook for about 5-7 minutes until browned and tender. Remove and set aside.
In the same pan, add the remaining 1 tablespoon butter. Add chopped onion and cook for 2-3 minutes until translucent. Stir in garlic and cook for another 30 seconds.
Add Arborio rice to the pan and stir for about 2 minutes until lightly toasted. Pour in the white wine and stir until mostly evaporated.
Start adding the warmed broth, ½ cup at a time, stirring constantly until absorbed. Continue adding broth gradually, stirring frequently. This process takes about 18-20 minutes.
Once the rice is creamy and al dente, stir in the cooked mushrooms, Parmesan cheese, salt, pepper, and thyme.
Add heavy cream. Remove from heat and let it rest for 2 minutes.