Lay the short rib rack on a cutting board bone-side down. Using a sharp boning knife, trim the thick top layer of fat and remove the silver skin beneath.
Flip the short rib rack over so the bones are facing up and slice into individual ribs. Slicing into individual ribs creates a larger surface area for smoke to penetrate and bark to form. The single ribs also make for more convenient serving because you can focus on slicing one rib at a time.
Divide the yellow mustard evenly between all ribs and rub it in evenly on all sides.
Season the short ribs evenly on all sides with rub.
Place a large foil pan on top of the Flavorizer bars, on the left side of the grill, below the cooking grate. Fill it halfway with room temperature water. Prepare the grill for cooking over low heat (275°F).
In a small bowl whisk the sauce ingredients. Refrigerate until ready to serve.
For an accurate reading, ensure that the probe tip is inserted 2 inches into the thickest short ribs, avoiding the bone.
Grill the short ribs, bone side down, above the foil pan, over low heat, with the lid closed.
When the bark is set remove the probes from the short ribs and leave them plugged into your device. This typically happens between an internal temperature of 165°F to 175°F. Remove the short ribs from the grill and wrap each rib with butcher paper.
Return the wrapped short ribs to the grill, above the foil pan. Insert the probe back into the same point of the short ribs and continue cooking until an internal temperature of 200°F to 205°F.
Remove the short ribs from the grill with tongs. Transfer the wrapped short ribs indoors to a dry, insulated cooler. Close the cooler and let the short ribs rest for 2 hours. Don't skip this step; it helps loosen the muscles and absorb moisture back into the short ribs.
While the ribs are resting make the sushi rice, following the instructions on the bag. Using a rice maker helps ensure perfectly done rice.
Remove the sushi rice from heat and let cool to room temperature. Prepare a bowl of water for prepping the nigiri pieces. The water will prevent the sushi rice from sticking to your hands.
Start by wetting your hands, then scoop a small portion of the rice into the palm of your hand. Roll the rice in the palm of your hand until it forms into a small oval shape, about 2 inches long. Set on a serving plate.
Layer the sauce over the top of each rice piece.
Remove the short ribs from the butcher paper. First cut the short rib off the bone, then thinly slice in the opposite direction, against the grain, into small pieces, about 1/8th thick.
Gently press the short rib slice on top of the rice and sauce, forming the beef onto the shape of the rice log.Â
Garnish with a small cilantro leaf and serve warm.
