Preheat your oven to 400°F. You want the oven good and hot before these go in, so get it started early. Line a baking sheet with foil for easy cleanup and give it a good spray with cooking spray so the meatballs won't stick.
Combine all of the ingredients in your stand mixer. Add the ground beef, breadcrumbs, Parmesan, eggs, salt, pepper, dried onion, and garlic to the mixing bowl. Use the regular paddle attachment — not the dough hook.
Mix on the lowest speed for about 30 seconds. This is important — you only want to mix until everything is just incorporated throughout the meat. As soon as you can see that it's all combined, stop the mixer immediately. Overmixing is the number one reason meatballs turn out tough instead of tender and juicy. If you don't have a stand mixer, you can absolutely do this by hand — just wash your hands well and mash it all together the way you would a meatloaf.
Scoop the meatballs onto your prepared baking sheet. I use a cookie scoop for this, and it works perfectly. It keeps them all a uniform size so they cook evenly. They won't look pretty at first, and that's fine — we're going to roll them next.
Roll each scoop into a ball with your hands. Just a quick squish and roll is all it takes. Leave a little bit of space between each meatball on the pan. They don't have to be perfectly the same size — a little variance is how you know they're homemade.
Bake at 400°F for 12–15 minutes. For meatballs about the size of a ping pong ball, 13–14 minutes is the sweet spot. Don't overbake them — remember, these are almost always going to get cooked again in a sauce, in the crockpot, or in whatever dish you're making. So we want them done but still nice and juicy on the inside.
Let them cool for 15–20 minutes before freezing. They don't have to be completely cool, but don't put them in the bag while they're still hot. Once they've cooled, just place them directly into a labeled freezer bag. Since they're pre-baked, they won't stick together — no flash freezing needed. You can grab a few at a time or use the whole bag.