01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - In a large 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 until just combined, being careful not to overwork the meat.
03 - Take roughly 2 tablespoons of the meat mixture and flatten it in your palm. Place a mozzarella cube in the center and shape the meat around the cheese, sealing it completely. Repeat with the remaining mixture.
04 - Arrange the stuffed meatballs on the prepared baking sheet. Bake for 20–22 minutes until fully cooked through and golden brown on the outside.
05 - While the meatballs bake, melt butter in a saucepan over medium heat. Whisk in flour and cook for 1–2 minutes to form a roux.
06 - Gradually whisk in 1 cup milk until smooth. Continue cooking, 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 is fully melted and the sauce is smooth. Season with salt and pepper to taste.
08 - Serve the hot meatballs drizzled with spicy cheese sauce. Garnish with additional chopped parsley if desired. Pair with crusty bread, pasta, or rice.