To freeze: Allow the meatballs to cool on the baking sheet and then freeze them for several hours. Don’t let them touch during freezing. If you can freeze them on the baking sheet, that works great. When fully frozen, toss them in a labeled resealable bag and store in the freezer. To reheat, just put them in the oven on a baking sheet at 350F for 20 minutes or until heated through.