To make the optional sauce, just whisk all the ingredients together and let stand at room temperature for 30-120 minutes.
How to make the pork belly and shrimp:
Sprinkle sugar over bottom of heavy large skillet NOT nonstick—the Feral Cooks use cast iron.
Place the skillet over medium heat without stirring, until sugar melts, then caramelizes to medium golden color, about 7 min.
Arrange pork belly strips in caramel in single layer. Pour 1/2 cup water over. Cook until water evaporates, turning pork occasionally, 12-14 min.
Add 1/2 cup more water. Cook until water evaporates again, turning pork occasionally, 12-14 min.
Add 1/2 cup water one final time. Cook until pork is tender, deep brown, and crisp and water has evaporated again.
Remove skillet from heat and remove pork to a plate.
Cut each pork strip in half, crosswise. Sprinkle lightly w/salt and generously w/pepper.
Return skillet w/drippings to med-high heat. Add shrimp and sauté until golden, turning once, about 2 min.
Return pork to skillet. Toss pork and shrimp until shrimp are just opaque in center, about 1 min.
Mound on platter. Sprinkle with optional onions and cilantro.
Serve w/rice and sauce. If possible, use Jasmine rice, as it has such a nice flavor.