01 -
Combine ground beef, breadcrumbs, milk, egg, minced onion, garlic, Worcestershire sauce, salt, and black pepper in a bowl. Mix gently until just incorporated. Shape into 3.8 cm diameter balls.
02 -
Heat a small amount of oil in a skillet over medium heat. Brown meatballs for 2 to 3 minutes per side until lightly seared.
03 -
In the same skillet, sauté sliced onions until softened, then add mushrooms and cook until browned.
04 -
Transfer sautéed onions, mushrooms, ketchup, Worcestershire sauce, and beef broth to the slow cooker. Nestle meatballs into the mixture.
05 -
Cook on low setting for 4 to 5 hours or on high for 2 to 3 hours until meatballs are fully cooked and flavors meld.
06 -
Mix cornstarch with cold water to create a slurry. Stir into slow cooker and cook on high for 20 minutes until gravy thickens.
07 -
Taste and adjust seasoning as needed. Serve warm, ideally over mashed potatoes or egg noodles.