01 - Preheat the 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 the 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 approximately 2 tablespoons of the meat mixture and flatten it in the palm of your hand. Place a mozzarella cube in the center and carefully wrap the meat around the cheese, rolling it into a ball to seal completely. Repeat with the remaining mixture and arrange on the prepared baking sheet.
04 - Bake for 20 to 22 minutes, or until the meatballs are fully cooked through and golden brown on the outside. The internal temperature should reach 160°F.
05 - While the meatballs bake, melt the 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 whisk in 1 cup milk, pouring slowly while whisking to prevent lumps. Continue cooking and stirring for 2 to 3 minutes until the mixture thickens to a creamy consistency.
07 - Reduce the heat to low. Add the grated cheddar, cayenne pepper, smoked paprika, and pickled jalapeños if using. Stir continuously until the cheese is completely melted and the sauce is smooth. Season with salt and pepper to taste.
08 - Arrange the hot meatballs on 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.