Soak the breadcrumbs: In a large bowl, combine the breadcrumbs with the milk and let sit for 5 minutes until softened into a paste. This keeps the meatballs moist instead of dense.

Mix the meat mixture: Add the ground beef, eggs, parmesan, garlic, onion, parsley, salt and pepper to the breadcrumb mixture. Mix gently with your hands just until combined, stopping as soon as the mixture holds together.

Shape the meatballs: With damp hands, roll the mixture into balls about 1.5 inches wide, roughly 2 tablespoons each. Set them on a tray as you go so they're ready to sear.

Heat the skillet: Warm the olive oil in a large skillet over medium-high heat until it shimmers. Work in batches so the meatballs aren't crowded.

Sear on all sides: Cook the meatballs for about 2 minutes per side, turning until they're browned all over, roughly 5 minutes total. They won't be cooked through yet, just browned.

Transfer to a baking sheet: Preheat the oven to 400°F. Move the seared meatballs to a parchment-lined baking sheet, spacing them an inch apart.

Bake until cooked through: Bake for 12-15 minutes, until the internal temperature reaches 165°F on a thermometer and the juices run clear when cut.

Warm the marinara sauce: While the meatballs bake, heat the marinara sauce in a saucepan over medium-low heat until it's gently bubbling.

Combine and simmer: Add the baked meatballs to the warm sauce and simmer together for 5 minutes so they soak up the flavor. Stir gently to coat without breaking them apart.

Serve or cool for freezing: Serve the meatballs hot over pasta or on their own, or let them cool completely on a tray before freezing for later.