01 - In a large mixing bowl, combine ground beef, breadcrumbs, milk, egg, chopped onion, minced garlic, Parmesan cheese, parsley, salt, and pepper. Mix gently until just incorporated, being careful not to overwork the meat.
02 - Roll the mixture into 1½-inch meatballs, yielding approximately 20 to 24 uniform portions.
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, then transfer to the slow cooker.
04 - Arrange the shaped 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 tender.
07 - Stir in the heavy cream. If the gravy needs thickening, drizzle in the cornstarch slurry while stirring, then cook on HIGH for an additional 10 to 15 minutes until the sauce reaches the desired consistency.
08 - Taste and adjust seasoning as needed. Serve hot over mashed potatoes, egg noodles, or steamed rice.