01 - Preheat oven to 400°F. Line a baking sheet with parchment paper and set aside.
02 - In a large mixing bowl, soak the breadcrumbs in 1/4 cup milk for 5 minutes. Add ground beef, ground pork, chopped onion, minced garlic, egg, parsley, salt, and black pepper. Gently mix with your hands until just combined, being careful not to overwork the meat.
03 - Scoop roughly 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 to form all the meatballs.
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 medium saucepan over medium heat. Whisk in the flour and cook for 1 to 2 minutes, stirring constantly to form a smooth roux.
06 - Gradually pour in 1 cup milk while whisking continuously to prevent lumps. Continue cooking and stirring for 2 to 3 minutes until the mixture thickens to a creamy consistency.
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 smooth. Season with salt and pepper to taste.
08 - Transfer the hot meatballs to a serving platter and drizzle generously with the spicy cheese sauce. Garnish with additional chopped parsley if desired. Serve alongside crusty bread, pasta, or rice.