01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - In a large mixing bowl, soak breadcrumbs in 1/4 cup milk for 5 minutes. Add ground beef, ground pork, onion, garlic, egg, parsley, salt, and black pepper. Mix gently until just combined, being careful not to overwork the meat.
03 - Portion roughly 2 tablespoons of the meat mixture, flatten it in your palm, and place a mozzarella cube in the center. Shape the meat around the cheese, rolling into a ball and sealing completely. Repeat with remaining mixture.
04 - Arrange meatballs on the prepared baking sheet. Bake for 20–22 minutes until fully cooked through and golden brown on the outside.
05 - While meatballs bake, melt butter in a saucepan over medium heat. Whisk in flour and cook for 1–2 minutes to form a smooth roux.
06 - Gradually whisk in 1 cup milk until smooth and no lumps remain. Cook, stirring constantly, until the mixture thickens, about 2–3 minutes.
07 - Reduce heat to low. Add cheddar cheese, cayenne, smoked paprika, and jalapeños if using. Stir until the cheese melts completely and the sauce is smooth. Season with salt and pepper to taste.
08 - Serve meatballs hot, drizzled generously with spicy cheese sauce. Garnish with fresh parsley if desired. Pair with crusty bread, pasta, or rice.