01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - In a large mixing bowl, soak the breadcrumbs in 1/4 cup milk for 5 minutes. Add ground beef, ground pork, onion, garlic, egg, parsley, salt, and black pepper. Gently mix until just combined, being careful not to overwork the meat.
03 - Scoop approximately 2 tablespoons of the meat mixture and flatten it in your palm. Place a mozzarella cube in the center and carefully 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 to 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 the flour and cook for 1 to 2 minutes, stirring constantly to form a smooth roux.
06 - Gradually whisk in 1 cup milk until smooth and free of lumps. Continue cooking and stirring for 2 to 3 minutes until the mixture thickens.
07 - Reduce heat to low. Add grated cheddar, cayenne pepper, smoked paprika, and pickled jalapeños if using. Stir until the cheese is fully melted and the sauce is silky smooth. Season with salt and pepper to taste.
08 - Serve the hot meatballs drizzled generously with spicy cheese sauce. Garnish with additional chopped parsley if desired. Pair with crusty bread, pasta, or rice.