In a large bowl, add ground beef, breadcrumbs, egg, chopped onion, garlic, salt, and pepper. Mix gently with your hands. Do not overmix. The mixture should feel soft and easy to shape.

Take small portions of the mixture. Roll them into medium-sized balls. Try to keep all meatballs the same size. This helps them cook evenly and look nice when serving.

Heat oil in a frying pan. Add meatballs and cook for a few minutes. Turn them gently until lightly brown on all sides. This step adds flavor but do not fully cook them yet.

Place sliced onions at the bottom of your slow cooker. These onions will become soft and sweet during cooking. They also add amazing flavor to the gravy.

Place the browned meatballs over the onions. Spread them evenly. Do not stack too much. This helps each meatball cook properly in the slow cooker.

In a bowl, mix beef broth, Worcestershire sauce, and ketchup. Stir well. This mixture creates the rich Salisbury gravy. Pour it evenly over the meatballs.

Cover the slow cooker with a lid. Cook on low for 4–6 hours. Do not open the lid often. The slow heat helps build deep flavor and tender meatballs.

In a small bowl, mix cornstarch with water. Add this mixture to the slow cooker in the last 30 minutes. Stir gently. The gravy will become thick and smooth.

Taste the gravy. Add salt or pepper if needed. Serve hot with mashed potatoes, rice, or bread. Enjoy your homemade comfort meal.