Step 1With a very sharp knife, score the skin of the pork belly in parallel lines one-fourth inch apart. If there is no skin, do the same with the layer of fat. Turn the pork belly over. Season with salt, pepper and fennel seed. Repeat with the skin side, but massage the seasonings into the skin. Let the pork rest at room temperature for 1 hour.
Step 2Peel the onions. Split them in half and cut lengthwise into slices just under one-half inch thick. Scatter the slices on a sheet pan with the garlic and rosemary. Place a rack over the onions and put the pork belly on the rack, skin side up.
Step 3Place the pork belly under the broiler, turning occasionally so it browns evenly on both sides. When the skin is brown and crisp, about 8 minutes per side, put the meat in a 350-degree oven. Cook for 45 minutes, then remove the onions, placing them in a saucepan and setting aside. Lower the heat to 300 degrees and cook for an additional 2 1/2 to 3 hours, until a skewer stuck through the meat pulls out with no resistance.
Step 4While the meat cooks, combine the kumquats, sugar, apricots, orange juice and ginger in a pot and simmer until the mixture reduces and thickens somewhat, about 50 minutes. Remove the ginger before serving. Set aside.
Step 5When the pork is done, remove the rack from the sheet pan and deglaze the pan with some of the chicken stock, scraping up the drippings. Pour the stock and scrapings into the saucepan with the onions. Add the veal demi-glace. Simmer until the sauce has reduced by one-third, to about 2 cups. Skim the fat. Strain.
Step 6To serve, thinly slice the pork belly. Ladle sauce onto each plate, then place two slices of meat topped with a spoonful of chutney on each. Sprinkle the pork with a little maple sugar and fleur de sel.