In a large bowl, combine the ground beef, Italian sausage, minced garlic, eggs, Worcestershire sauce, breadcrumbs, Parmesan cheese, Italian seasoning, and a generous pinch each of salt and black pepper. Mix gently with your hands until just combined—don't overwork the mixture, as this will make the meatballs tough and dense. The key is to blend everything evenly without compressing the meat too much, which keeps them tender and light.

Roll the meatball mixture into 1.5 to 2-inch balls using lightly dampened hands to prevent sticking—I find this makes the process much cleaner and faster. Arrange them on a foil-lined baking sheet in a single layer. Broil at 500°F for about 8 minutes, until the outsides are browned and set. This step isn't about cooking them through, but rather developing a flavorful crust that will keep them intact when they simmer in sauce.

Carefully transfer the broiled meatballs to a 6-quart slow cooker. Pour both jars of marinara sauce over them, gently stirring to coat evenly. Make sure the meatballs are mostly submerged or at least well-coated with sauce to prevent them from drying out during cooking.

Cover the slow cooker and cook on high for 4 hours or on low for 8 hours. I prefer the low and slow method when time allows—it allows the flavors to meld beautifully and keeps the meatballs incredibly tender without any risk of them becoming tough. Check occasionally and gently stir to ensure even cooking, though this isn't strictly necessary.