Whisk together toyomansi and sukang maasim. Add garlic, peppercorns, bay leaves, kumquats and pork belly. Marinate for 24 hours.
Preheat oven to 300°F. Place marinated belly in a pot or braising pan and pour marinade over. Add chicken stock. Bring to a simmer on the stovetop, cover loosely with foil and then transfer to the oven. Braise 2½ hours or until pork belly is very soft. Remove from oven and let braised belly cool in the braising liquid until it is room temperature.
Once belly has cooled to room temperature, remove from liquid and place on a flat baking sheet. Cover with wax or parchment paper and top with another baking sheet and about 2 pounds of weight (canned beans or vegetables work well). Reduce braising liquid until it is thick enough to coat the back of a spoon. Strain liquid to remove solids.
Cut compressed belly into 6 portions. Heat a heavy-bottomed sauté pan and add belly, fat side down. Render fat, basting frequently, until fat side is crispy and the meat is hot throughout.
Serve over rice, topped with sauce and cilantro, with kumquat halves on the side.
*Look for toyomansi and sukang maasim at Asian grocery stores.
Related Recipes: Local Ingredients, Global Roots.