Normally sliders are small burgers, but these, made with pork belly, take the concept to a new level.
My buddy Shane worked at Momofuku Noodle Bar, a restaurant on First Avenue in New York, where they serve something similar, and although I was inspired by that sandwich, it is nothing like mine, which is more like an upscale White Castle burger.
The little piece of pork fat melts in the mouth.
To make the caramelized onions: In a large skillet, melt the butter over medium-high heat.
When hot, add the onions and cook, stirring, until soft and translucent, 6 to 7 minutes.
Sprinkle with the sugar and cook until lightly browned and caramelized, 2 to 4 minutes.
Preheat the oven to 375° F.
To make the sandwiches: With a small, sharp knife, score the fatty side of the pork belly and then cut the pork into 4 equal square pieces.
Season lightly with salt and pepper.
In a large Dutch oven or similar pot, heat the canola oil over medium heat.
When hot, cook the pork belly, 1 piece at a time and scored side down, until most of the fat renders, about 4 minutes; do not increase the heat or the pork belly will cook too quickly.
Remove each piece of pork belly from the pot when cooked.
Drain all but 4 tablespoons of fat from the pot and cook the garlic over medium heat, stirring, until lightly browned, about 1 minute.
Add the onion and cook, stirring, until lightly colored, 2 to 3 minutes.
Add the brown sugar and vinegar and cook, stirring, until syrupy, 1 to 2 minutes.
Whisk in the mustard until smooth.
Stir in the beef and chicken broths and the rosemary leaves and bring to a boil over high heat.
Add the pork belly, cover the pot, and put in the oven.
Braise for 1 1/2 to 2 hours, until the pork is fork-tender.
Lift the pork belly from the pot and transfer to a plate.
Do not turn off the oven.
Discard the cooking liquid.
Brush each halved roll with the olive oil and grill on a heated countertop grill or under a hot broiler for 2 to 3 minutes or until toasty and slightly charred.
Cut each square of belly in half and put 1 piece on the bottom half of each slider roll.
Top with a few slices of cheese.
Put these assembled sandwich halves on a baking sheet and bake for 1 to 2 minutes at 375° F or until the cheese melts and begins to brown.
Remove from the oven and top with the caramelized onions.
Spread the top halves of the rolls with the mayonnaise and press on top of the onions to close the sandwiches.