Dice onion and mince garlic. Place in a baggie or bowl and refrigerate until using. Slice mushrooms and place in a separate container; refrigerate until using.
+ 20 – 25 minutes cooking time Heat olive oil and butter in a large skillet over medium-high heat. Add onion and garlic and cook for 3 minutes. Add mushrooms and cook another 3 minutes. Stir in rice and continue cooking for another 3 minutes. Season with 1/2 t. salt and 1/4 t. pepper.
Slowly pour in beef stock while constantly stirring. Reduce heat to medium. Continue cooking for 20-25 minutes, until creamy and rice is tender, stirring well at least every 3-5 minutes.
Season to taste with additional salt and pepper. Sprinkle with grated Parmesan cheese before serving.