In a medium bowl, combine the ground beef, ? cup diced onion, 2 minced cloves garlic, the bread crumbs, milk, Worcestershire sauce, mustard, salt, and pepper. Mix well and form the mixture into 16 evenly sized balls.

Place a large oven-safe skillet over medium heat and mist with cooking spray. Add the meatballs and cook until browned on all sides, about 8-10 minutes. Remove the meatballs to a clean plate and cover to keep warm.

In the same skillet, add the olive oil and swirl to coat. Add the onions and cook until tender, about 7-8 minutes.

Add the minced garlic and cook for 30 seconds until fragrant.

In a measuring cup, whisk the cornstarch into the broth until dissolved, then pour into the skillet. Scrape up any browned bits on the bottom of the pan.

Increase heat to high and bring the gravy to a boil, stirring constantly. Once boiling, reduce heat to medium and cook until thickened, about 4-5 minutes, stirring constantly.

Return the meatballs to the gravy and spoon the gravy over them.

Remove from heat and top with shredded cheese. Allow to rest for 5 minutes for the cheese to melt.

Optional: for browner cheese, place under the oven broiler for 1-2 minutes, watching carefully.

Garnish meatballs with chopped fresh parsley if desired.