01 -
In a large mixing bowl, combine the ground beef, breadcrumbs, Parmesan cheese, egg, garlic powder, onion powder, salt, and pepper. Mix gently until evenly incorporated, being careful not to overmix. Form into approximately 20 meatballs (2.5cm diameter) and set aside.
02 -
Melt the butter in a skillet over medium heat. Add the sliced onions and cook, stirring frequently, until golden brown and caramelized (15-20 minutes). Deglaze the skillet with a splash of beef broth, scraping up any browned bits. Transfer the caramelized onions to the slow cooker.
03 -
Place the meatballs on top of the caramelized onions. Pour in the remaining beef broth, Worcestershire sauce, and thyme. Gently stir to coat the meatballs in the sauce.
04 -
Cover and cook on low for 4-5 hours or high for 2-3 hours, until the meatballs are fully cooked and tender.
05 -
Once the meatballs are cooked, sprinkle the shredded cheese over the top. Cover and cook for an additional 10-15 minutes on low, until the cheese is melted and bubbly.