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 wrap the meat around it, sealing all edges to fully enclose the cheese. Roll between your palms to form a smooth ball. Repeat with the remaining mixture and arrange on the prepared baking sheet.
04 - Bake for 20–22 minutes until the meatballs are fully cooked through and golden brown on the outside.
05 - While the meatballs bake, melt the butter in a medium saucepan over medium heat. Whisk in the flour and cook, stirring constantly, for 1 to 2 minutes to form a smooth roux.
06 - Gradually whisk in 1 cup milk, stirring constantly to prevent lumps. Continue cooking and stirring until the mixture thickens, about 2 to 3 minutes.
07 - Reduce heat to low. Add grated cheddar, cayenne pepper, smoked paprika, and pickled jalapeños if using. Stir until the cheese is completely melted and the sauce is smooth and creamy. Season with salt and black pepper to taste.
08 - Transfer the hot meatballs to a serving dish and generously drizzle with the spicy cheese sauce. Garnish with additional chopped parsley if desired. Serve alongside crusty bread, pasta, or rice.