Preheat the oven. Set it to 425°F (220°C). Line a rimmed baking sheet with foil for easy cleanup and place a wire rack on top.
Lightly oil the rack. The rack helps fat drip away and promotes even browning.
Make a panade. In a large bowl, combine the breadcrumbs and milk. Stir and let it sit for 2–3 minutes until the crumbs absorb the liquid.
This keeps the meatballs tender.
Add aromatics and seasonings. Mix in the egg, grated onion (with any juices), garlic, Parmesan, parsley, oregano, salt, pepper, and red pepper flakes. Stir until well combined.
Add the meat. Break the ground beef and pork into chunks and add to the bowl. Using your hands, gently mix just until evenly combined. Do not overwork or the meatballs can turn tough.
Shape the meatballs. Lightly oil your hands.
Roll into 1.5-inch (4 cm) balls, about 2 tablespoons each. You should get 20–24 meatballs. Place them on the prepared rack with a little space between each.
Brush with oil. Lightly brush or mist the tops with olive oil.
This encourages an even, golden crust in the oven.
Bake. Bake for 15–18 minutes until the meatballs are cooked through and the tops are nicely browned. For extra color, switch to broil for the last 1–2 minutes, keeping a close eye to avoid burning.
Check doneness. Internal temperature should reach 160°F (71°C) for beef/pork. If you don’t have a thermometer, cut one open to ensure it’s no longer pink in the center and juices run clear.
Rest. Let the meatballs sit on the rack for 5 minutes.
This helps the juices redistribute and the crust set.
Serve. Toss with warm marinara, spoon over creamy polenta, stuff into toasted sub rolls, or serve with tzatziki and a salad. Finish with a sprinkle of Parmesan and fresh parsley.