Unlike other ground beef recipes like a burger, meatballs need to be cooked all the way through. We don't want meatballs with any pink inside like you'd get with a medium or medium rare steak. From experience, I've found that baking in a 400 degree oven for about 20-22 minutes will get the best results with a done meatball. If you're baking in a sauce you may need to leave them in a little longer.