Preheat the oven to 425°F (218°C).
In a separate large mixing bowl, combine the ground beef, Polidori hot Italian sausage (removed from casings), minced garlic, eggs, freshly grated Parmesan and Mozzarella cheeses, Italian seasoning, grated onion, Worcestershire sauce, Kosher salt, black pepper, and red pepper flakes.
Add the prepared panade mixture (breadcrumb and milk mixture) into the bowl with the meatball ingredients.
Mix and Shape Meatballs. Using your hands or a spoon, gently mix all the ingredients until well combined, ensuring the panade is evenly distributed throughout the meat mixture.
Use a 2-ounce scooper or your hands to portion out the meat mixture and roll it into meatballs, shaping them evenly.
Place the meatballs on a foil-lined half sheet tray (18x13 baking sheet), leaving a bit of space between each meatball to allow for even cooking.
Bake the Meatballs. Place the tray of shaped meatballs into the preheated oven.
Bake at 425°F (218°C) for 10-12 minutes or until the meatballs are fully cooked through and nicely browned on the outside.
Once cooked, remove the meatballs from the oven. Serve the delicious, moist, and flavorful Polidori Sausage Perfect Meatballs on their own as appetizers, with pasta, in sandwiches, or however you prefer!