In a bowl, mix ground beef, breadcrumbs, egg, garlic, onion, milk, salt, and pepper.
Roll mixture into medium-sized meatballs.
Heat oil in a skillet over medium heat. Brown meatballs on all sides. Remove and set aside.
In the same skillet, melt butter and cook mushrooms until soft and golden.
Add garlic and cook for 30 seconds.
Pour in beef broth and let it simmer for a few minutes.
Add heavy cream and parmesan cheese. Stir until the sauce thickens.
Return meatballs to the skillet. Simmer for 10–15 minutes until fully cooked.
Garnish with fresh parsley and serve warm.