01 - In a large bowl, combine ground beef, breadcrumbs, milk, egg, chopped onion, minced garlic, Parmesan cheese, parsley, salt, and black pepper. Mix gently until just combined, being careful not to overwork the meat.
02 - Roll the mixture into 1 1/2-inch meatballs, yielding approximately 20 to 24 uniform pieces.
03 - For enhanced flavor and texture, heat a thin layer of oil in a skillet over medium-high heat. Brown the meatballs in batches, approximately 2 to 3 minutes per side, until a golden crust forms. Transfer to the slow cooker.
04 - Arrange all meatballs in an even layer at the bottom of the crockpot.
05 - In a separate bowl, whisk together beef broth, cream of mushroom soup, Worcestershire sauce, soy sauce, dried thyme, onion powder, and garlic powder until smooth. Pour the mixture evenly over the meatballs in the slow cooker.
06 - Cover and cook on LOW for 4 to 5 hours or on HIGH for 2 to 3 hours, until the meatballs are cooked through and reach an internal temperature of 160°F.
07 - Stir in the heavy cream. If the gravy is too thin, add the cornstarch slurry, stirring well to incorporate. Cook on HIGH for an additional 10 to 15 minutes until the gravy thickens to your desired consistency.
08 - Taste and adjust seasoning as needed. Serve hot over mashed potatoes, egg noodles, or steamed rice.