Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.

In a large mixing bowl, combine ground beef, breadcrumbs, egg, onion, garlic, Worcestershire sauce, salt, pepper, and thyme. Mix gently.

Roll the mixture into 1-inch meatballs and place them on the baking sheet. Bake for 20 minutes.

Heat olive oil in a skillet over medium heat. Sauté onions and garlic for 5-7 minutes.

Add beef broth and Worcestershire sauce to the skillet, simmer and gradually whisk in cornstarch until thickened.

In a pot, boil chopped Yukon Gold potatoes and garlic until fork-tender. Drain and evaporate excess moisture.

Mash the potatoes with milk, butter, salt, pepper, and chopped parsley until smooth.

Toss the baked meatballs in the gravy. Serve over mashed potatoes, garnished with parsley.