Preheat and prep: Heat the oven to 400°F (200°C) if baking. Line a sheet pan with parchment or lightly oil it. If pan-searing, set a large skillet on the stove and have oil ready.
Soak the breadcrumbs: In a large bowl, combine breadcrumbs and milk.
Stir and let sit for 3–4 minutes until the crumbs are hydrated and soft. This simple step keeps the meatballs tender.
Add aromatics and seasonings: To the bowl, add grated onion, minced garlic, Parmesan, parsley, salt, black pepper, and red pepper flakes if using. Mix gently to distribute.
Add pork and egg: Add the ground pork and crack in the egg.
Using a fork or your hands, mix until just combined. Do not overwork the meat—stop as soon as everything looks evenly mixed.
Shape the meatballs: Lightly oil your hands. Scoop 2-tablespoon portions and roll into balls about 1 1/2 inches wide.
You should get around 20–24 meatballs. Place them on the sheet pan or a plate.
Choose your cooking method: To bake: Arrange on the prepared pan with a little space between them. Bake 14–18 minutes, until browned and the centers reach 160°F (71°C).
To pan-sear: Heat 2 tablespoons olive oil over medium heat.
Add meatballs in batches without crowding. Brown on all sides, 6–8 minutes total, then cover and cook 2–3 minutes more, or finish in a 350°F (175°C) oven for 5 minutes. Check for 160°F (71°C) inside.
Optional sauce simmer: If serving with marinara, warm the sauce in a skillet or pot.
Add cooked meatballs and let them simmer 5 minutes to meld flavors.
Serve: Top with extra Parmesan and parsley. Serve with pasta, crusty bread, polenta, or a simple salad.