01 - In a large mixing bowl, thoroughly blend ground beef, breadcrumbs, Parmesan cheese, egg, minced garlic, salt, and black pepper until evenly incorporated.
02 - Form the mixture into even, bite-sized balls and carefully arrange them in an even layer inside the slow cooker insert.
03 - In a separate bowl, whisk together marinara sauce, balsamic vinegar, and brown sugar until the sugar is dissolved and the sauce is uniform.
04 - Pour the balsamic glaze evenly over the arranged meatballs. Cover and cook on low setting for 4 to 5 hours, or until meatballs are thoroughly cooked and tender.
05 - Carefully transfer the meatballs and glaze to a serving platter. Serve warm, accompanied by cooked pasta or fresh crusty bread if desired.