Preheat oven to 475 degrees. In a large bowl, combine beef, pork, panko, 1/2 cup milk, eggs, garlic, 1 tablespoon salt, 1/2 teaspoon pepper, and allspice. Mix just until combined.
Using a rounded 1-tablespoon measure for each, form mixture into meatballs (you should have about 48). Place meatballs onto two rimmed baking sheets; bake until golden brown and cooked through, 10 to 12 minutes, rotating sheets halfway through.
Meanwhile, make sauce: In a medium saucepan, melt butter over medium-high. Add flour; cook, whisking, 1 minute (do not let darken). Gradually whisk in remaining cup milk and broth; bring to a boil. Reduce heat, and simmer until sauce has slightly thickened, 2 to 3 minutes. Transfer to a large bowl.
Using a slotted spoon, add meatballs to bowl with sauce; gently toss to combine. Serve as an appetizer, on toothpicks, with jelly on the side; or as a main, over noodles, garnished with parsley, with jelly on the side.
Divide meatballs and sauce among airtight containers; freeze up to 3 months. Thaw overnight in refrigerator (or place containers under cold running water to release frozen blocks). Reheat, thinning sauce with water if necessary.