Add frozen meatballs to crockpot. Add chili sauce and grape jelly. Cover and cook for 2 to 3 hours on HIGH or 4 to 6 hours on LOW, until the sauce is hot. Serve directly from the crockpot with a serving spoon or toothpicks, or transfer to a serving dish.
To sauce the meatballs on the stovetop:
Add meatballs to saucepan. Add chili sauce and grape jelly. Cover and simmer over medium heat until the sauce is hot, about 10 minutes.
In a large bowl, combine beef, pork, bread crumbs, onion, milk, egg, Worcestershire sauce, 1 teaspoon salt, and 1/2 teaspoon pepper.
Using a strong spatula or your hands (I like to wear latex gloves), mix well. Shape the mixture into 1-inch balls (you should have around 48 total).
To fry the meatballs:
Heat vegetable shortening in a large skillet over medium-high heat. Fry the meatballs in batches until browned on all sides and the meatballs are cooked, about 5 to 7 minutes per batch (an internal thermometer should read 155 degrees for 15 seconds). Add more shortening between batches if the skillet looks dry.
To bake the meatballs:
Preheat oven to 400 degrees. Line a rimmed baking sheet with foil and set a rack on top. Arrange meatballs on rack and bake until browned with crispy edges, about 20 minutes (an internal thermometer should read 155 degrees for 15 seconds).
Sweet chili sauce may be substituted for regular chili sauce. The flavor will be a little different but still delicious!
Adapted from "Appetizer Meat Balls" in the Calico Capers Go To Cookbook.