Preheat the oven to 400°F (200°C). Combine ground beef, breadcrumbs, egg, onion, garlic, Worcestershire sauce, salt, pepper, and thyme in a bowl. Mix gently.

Shape the mixture into 1-inch meatballs and place them on a parchment-lined baking sheet. Bake for 20 minutes until golden brown and cooked through.

In a skillet, heat olive oil and sauté onion and garlic for 3-4 minutes until translucent. This builds flavor for the gravy.

Add beef broth and a splash of Worcestershire sauce to the skillet. Simmer, then whisk cornstarch and water separately and add to the skillet to thicken the gravy.

In a large pot, boil water and add chopped Yukon Gold potatoes and garlic. Cook for 15-18 minutes until fork-tender.

Drain the potatoes and return them to the pot. Add milk, butter, salt, pepper, and parsley. Mash until smooth and creamy.

Toss the baked meatballs in the prepared gravy to coat them. Serve the meatballs over the mashed potatoes with extra gravy on top.