Prepare pork 1 day ahead of time: Place pork on work surface, skin-side-up. Using pricking tool, prick pork skin, making small holes that just puncture the surface all over meat. Set pork aside. Dissolve baking soda in 5 cups boiling water. Transfer water to cup with pouring spout. Grasp one corner of the pork belly with tongs. Holding pork belly over sink, slowly pour baking soda liquid over pork skin to scald it. Transfer pork to work surface, skin-side-down. Using sharp knife, score the meat, making 1-inch-deep parallel slits, 1 1/2 inches apart.
Combine 3 tablespoons rice wine, brown sugar, salt and five-spice powder in small bowl and distribute evenly over meat, rubbing mixture into slits. Transfer pork, skin-side-up, to baking dish. Wipe any moisture from skin with paper towel and refrigerate overnight, uncovered.
Preheat oven to 375°F. Thread 3 metal skewers horizontally through meat layer of pork belly to prevent it from curling. Transfer pork, skin-side-up, to rack set over foil-lined roasting pan. Wipe moisture from skin with paper towel. Brush remaining 2 tablespoons rice wine over skin. Pour hot water into pan to depth of 1/4 inch. Place pan on center oven rack and roast pork about 1 hour, until a meat thermometer inserted into thickest part reads 160°F. Reset heat to broil and cook until skin is blistered and browned, 5-10 minutes. Remove pork from oven; let rest for 15 minutes before slicing. Slice 2-3 slices of pork belly per sandwich (8 to 12 slices total); set aside.
For pineapple bourbon chutney: Heat vegetable oil in skillet over medium heat. When hot, add onions; cook until caramelized, about 5-7 minutes. Add bourbon to pan and cook until liquid has reduced. Add pineapple, ginger and red pepper flakes to pan; cook until pineapple softens, about 3 minutes. Stir in brown sugar, cook, stirring occasionally for 5-7 minutes or until mixture thickens. Remove from heat and cool.
For assembly: Heat large skillet over medium heat and heat reserved pork belly slices until warm throughout and slightly crispy on both sides. Set aside. Butter outside of each pretzel roll slice. On inside of each roll top 1 side with 2 slices chipotle jack cheese and the other with 2 slices sharp cheddar. Place 2 to 3 slices of pork belly over bottom roll. Dividing evenly, spread chutney over pork belly. Top each sandwich with remaining roll slice, butter-side-up.
Preheat skillet or griddle; briefly brown both sides of each sandwich over medium-low heat. Then grill 1 side of sandwiches until golden, about 3 to 5 minutes. Carefully flip sandwiches; cover skillet with lid; grill until second side is golden brown and cheese is fully melted, about 5 minutes.
For Pork Belly:
- 4 pounds 1 3/4-inch thick slab pork belly
- 1 1/2 tablespoons baking soda
- 5 tablespoons Chinese rice wine, divided
- 3 tablespoons light brown sugar, packed
- 1 tablespoon sea salt
- 1 1/4 teaspoons Chinese five-spice powder
For Pineapple Bourbon Chutney:
- 2 teaspoons vegetable oil
- 1/4 cup yellow onion, minced
- 1 tablespoon bourbon
- 1 1/2 cups fresh pineapple, diced
- 1 teaspoon fresh ginger, grated
- 1/2 teaspoon red pepper flakes
- 1/3 cup light brown sugar, packed