Preheat the oven to 375 degrees F. Line a baking sheet with aluminum foil. Combine the ground beef, bread crumbs, milk, onion, eggs, and salt in a bowl. Mix well. Form the meat into 1-inch balls and place on the baking sheet. Place the baking sheet in the oven and bake at 375 degrees F for 25-30 minutes or until browned and cooked through. Let the meatballs cool (you can transfer them to a wire rack if there is a lot of grease on the baking sheet) then divide them between freezer-safe containers. Store in the freezer for up to 3 months. Let thaw before adding to your favorite recipes.