The key to tender meatballs is fresh breadcrumbs. Pulse torn bread slices in a food processor until the crumbs are fine. You can store fresh breadcrumbs in your freezer.
Set your oven rack in the middle of the oven and turn the oven to broil. Broil on high for 10-12 minutes, until the tops are browned. Once cool, you can freeze any extra meatballs.
In a braiser or dutch oven, saute onions and garlic in olive oil. Add some crushed red pepper flakes, a bit of sugar, crushed tomatoes, and tomato puree. Season with salt and peppeer.