Preheat the oven to 375°F (190°C). Line a baking sheet with parchment paper.
STEP 2
In a large bowl, combine ground beef, ground pork, panko, onion, milk, egg, salt, garlic, and pepper. If mixture is too wet, refrigerate for 15-20 minutes to firm up. Shape into 24 meatballs (about 1.5 inches) and place on the baking sheet.
STEP 3
Bake meatballs in the preheated oven until no longer pink (about 20 minutes). Internal temperature should reach 165°F (74°C).
STEP 4
Prepare apple butter bourbon glaze. In a small saucepan, whisk together apple butter, bourbon, soy sauce, maple syrup, and mustard. Simmer over medium-low heat, stirring frequently, until smooth and thickened (5-7 minutes).
STEP 5
Remove meatballs from the oven and transfer to a large bowl. Pour glaze over meatballs and gently toss to coat. Serve warm.