In a large bowl, combine ground beef, garlic, parsley, bread crumbs and egg. Using your hands, combine all ingredients. Add salt and pepper to your liking.
Shape into meatballs (approximately 1.5 to 2 inches in diameter).
Place meatballs on a cookie sheet and bake at 350 degrees Fahrenheit for 20 minutes, or until browned and cooked through, turning the meatballs every 5-10 minutes.
In a large skillet, heat up olive oil over medium heat, and add sliced mushrooms. Cook until mushrooms get soft. Season with salt and pepper. When the mushrooms are almost done, slowly stir in heavy cream. Stir for 1 to 2 minutes, allowing the cream to reduce and absorb into the mushrooms.
Serve meatballs on a large serving platter and top with mushroom sauce.
Sprinkle with parsley and serve immediately.