1. Prepare Oven, Baking Sheet, and Soak Breadcrumbs:

• Gather all your ingredients.
• Cover a large baking sheet with aluminum foil and spray the foil lightly with cooking spray. Set aside.
• In a small bowl, combine the ⅓ cup plain bread crumbs and ½ cup milk (or beef broth). Stir briefly and let the bread crumbs soak for about 20 minutes to absorb the liquid.

2. Sauté the Onions:

• While the breadcrumbs soak, heat the 2 tablespoons of olive oil in a medium skillet over medium heat.
• Add the diced onion to the skillet. Cook and stir until the onion has softened and turned translucent, about 5 minutes.
• Reduce the heat to low and continue cooking and stirring the onion until it is very tender and sweet, about 15 minutes more. Do not rush this step; well-cooked onions add significant flavor. Remove from heat and let cool slightly.

3. Combine Meatball Mixture and Chill:

• In a large mixing bowl, gently combine the 1 pound of ground beef and 1 pound of ground pork using your hands or a spatula. Try not to overwork the meats at this stage.
• Add the slightly cooled sautéed onions, the soaked bread crumb mixture (it should be like a paste), the lightly beaten eggs, grated Parmesan cheese, chopped fresh parsley, crushed/minced garlic, 2 teaspoons salt, 1 teaspoon black pepper, 1 teaspoon dried Italian herb seasoning, and optional ½ teaspoon red pepper flakes to the bowl with the ground meats.
• Gently mix all the ingredients together using a rubber spatula or your clean hands until just combined. Be very careful not to overmix, as this can result in tough meatballs.
• Cover the bowl with plastic wrap and refrigerate the meatball mixture for about one hour. Chilling helps the flavors meld and makes the mixture easier to shape.

4. Preheat Oven and Form Meatballs:

• Towards the end of the chilling time, preheat the oven to 425°F (220°C).
• Remove the chilled meatball mixture from the refrigerator.
• Using your hands (lightly moistened can prevent sticking) or a cookie scoop (about 1.5 to 2 tablespoons per meatball), form the mixture into balls about 1 ½ inches in diameter.
• Arrange the formed meatballs in a single layer on the prepared foil-lined and sprayed baking sheet, ensuring they are not touching.

5. Bake the Meatballs:

• Place the baking sheet with the meatballs into the preheated oven.
• Bake for 15 to 20 minutes, or until the meatballs are nicely browned, cooked through, and an internal temperature of 160-165°F (71-74°C) is reached on a meat thermometer.

6. Serve:

• Carefully remove the baked meatballs from the oven.
• Serve hot with your favorite tomato sauce over spaghetti, in meatball sub sandwiches, or as appetizers. Enjoy!