Koji Prime Rib

Ingredients

• 1 standing rib roast, 7 to 12 pounds
• 1 cup shio koji
• Freshly ground black pepper
• For serving:
• Koji beef jus, optional

Directions

1. The day before you plan to roast, take a sharp knife and separate the meat from the ribs in 1 piece, working the blade as close to the bones as you can. Set the rib bones aside. Blot the roast well with paper towels, then use your hands to coat the roast and the bones all over with shio koji. Set the meat back onto the bones, then secure everything with butcher’s twine so it has its original roast shape again. Put the roast on a wire rack, fat cap facing up, over a foil-lined rimmed baking sheet, and chill it uncovered for at least 12 hours and up to 24 hours.
2. When you’re ready to cook, set a rack in the middle of the oven and heat it to 225 degrees F (105 degrees C). With a paper towel, lightly brush off any extra shio koji bits from the fat cap. Move the baking sheet, rack, and roast into the oven, and roast until an instant-read thermometer inserted into the thickest part reads 125 degrees F (52 degrees C) if you want medium-rare, or 135 degrees F (57 degrees C) if you want medium, which should take 4 to 5 hours.
3. Take the roast out of the oven, cover it loosely with foil, and leave it at room temperature to rest for at least 30 minutes and up to 1 1/2 hours. While it rests, turn the oven up to 500 degrees F (260 degrees C), or as hot as your oven will go.
4. About 10 minutes before serving, uncover the roast and return it to the very hot oven. Let it cook until the outside is crisp and richly browned, 6 to 10 minutes. Pull it from the oven and move the roast to a carving board.
5. To serve, snip off the twine and lift the roast away from the ribs. Use a sharp knife to slice between the ribs, separating them into individual pieces, then cut the roast into 3/4-inch-thick slices. Serve right away, with coarse sea salt and koji beef jus, if using, passed at the table.