Start by gathering all your ingredients to ensure a smooth cooking process. Preheat your oven to 425°F (220°C) while you line a baking sheet with foil and coat it lightly with cooking spray.

In a mixing bowl, combine the plain bread crumbs with milk. Allow the mixture to soak for about 20 minutes.

Heat olive oil in a skillet over medium heat. Add the finely diced onion and sauté until soft, about 5 minutes. Cook for another 15 minutes until the onions are very tender.

In a large mixing bowl, combine the ground beef and ground pork. Add the sautéed onions, soaked bread crumb mixture, large eggs, grated Parmesan cheese, fresh parsley, crushed garlic, salt, black pepper, Italian herbs, and red pepper flakes. Mix gently until just combined, then refrigerate the mixture for 1 hour.

Once chilled, shape the mixture into 1.5-inch meatballs and arrange them on the prepared baking sheet.

Place the baking sheet in the oven and bake the meatballs for about 15-20 minutes until browned and cooked through.

Once baked, remove the meatballs from the oven and let them cool slightly. Serve over pasta, in a sub sandwich, or enjoy straight from the baking sheet.