Preheat oven to 375°F (190°C). Lightly grease a baking sheet or line with parchment paper.
In a large bowl, combine the ground beef, breadcrumbs, milk, egg, chopped onion, salt, and pepper. Mix gently until just combined. Do not overmix.
Roll the meat mixture into 1-inch meatballs and place them on the prepared baking sheet.
Bake for 15-20 minutes, or until the meatballs are cooked through and browned.
While the meatballs are baking, prepare the sauce. In a medium saucepan, combine the chopped cranberry sauce, orange marmalade, ketchup, Worcestershire sauce, and garlic powder. Stir to combine.
Heat the sauce over medium heat, stirring occasionally, until it is warm and well combined. Do not boil.
Add the baked meatballs to the saucepan with the sauce. Stir gently to coat the meatballs.
Simmer for another 5-10 minutes, allowing the flavors to meld and the meatballs to heat through.
Serve hot with toothpicks for easy serving.
Notes
These are best served warm as an appetizer. They can also be made ahead of time and reheated gently in the sauce.