For the Ribs: Adjust oven rach to middle position and heat oven to 250 degrees. With tip of paring knife, loosen membrane on underside of each rach of ribs. Grab membrane with paper towel and pull it off slowly in a single piece. Combine remaining ingredients in a large roasting pan. Add ribs to pan, turning to coat both sides, and arrange meaty side down. Cover pan tightly with foil and cook until just tender, 2.5-3 hours Transfer ribs to a large plate.
For the Glaze: Strain 3 cups cooking liquid from roasting pan into large nonstick skillet, and discard solids and remaining liquid. Do not wash roasting pan. Using wide spoon, skim fat from liquid. Stir in jelly and vinegar. Bring to simmer over medium high heat and cook until syrupy and reduced to 2 cups, about 15-20 minutes. Off heat, stir in cilantro and cayenne.
Heat broiler (do not raise oven rack). Pour enough water into roasting pan to cover bottom and fit pan with a flat roasting rack. Reserve 1/2 cup glaze for serving. Arrange ribs on rack meaty side down and brush with glaze. Place roasting pan back on middle rack in oven and broil until beginning to brown, 2-4 minutes. Flip ribs over, brush with more glaze, then broil, brusing ribs with glaze every 2-4 minutes until ribs are deep mahogany color, 9-12 minutes. Transfer ribs to cutting board, tent with foil and let rest 10 minutes. Slice between bones, transfer ribs to platter, brush with reserved glaze. Sprinkle with scallions. Serve.