Prepare all ingredients: slice mushrooms, mince garlic, chop onion, and warm broth in a separate pan.
Heat 1 tablespoon olive oil and 1 tablespoon butter in a large pan. Sauté mushrooms with a pinch of salt until browned, about 8 to 10 minutes, then set aside.
In the same pan, add remaining olive oil and sauté onion until translucent, about 3 to 4 minutes. Add garlic and cook for 30 seconds.
Add Arborio rice and stir to coat with oil and butter. Toast for 1 to 2 minutes until edges become translucent.
Pour in white wine and stir until it is fully absorbed by the rice.
Add warm vegetable broth one ladle at a time, stirring frequently. Allow each addition to be absorbed before adding more, continuing for 18 to 20 minutes.
Stir in the cooked mushrooms and let them heat through for 3 minutes.
Turn off heat and stir in Parmesan cheese, a knob of butter, and an optional splash of heavy cream. Season with salt and pepper to taste.
Serve hot, garnished with chopped parsley and an optional drizzle of truffle oil.