Prepare the Prime Rib

Trim and Salt:

• If your roast has bones, use a boning knife to carefully remove them. Ask your butcher if you're unsure. Save the bones for additional flavor during roasting.
• Trim excess fat, leaving a thin layer to retain moisture. This step ensures the crust adheres properly during cooking.
• Generously salt the roast all over. Place it on a rack set on a cookie sheet and refrigerate uncovered for several hours or up to 48–72 hours. This step helps the salt penetrate the meat and dries the surface for a better crust.

Preheat Oven to 250°F / 120°C 

Make the Breadcrumb Crust:

• Grate Pecorino Romano and Parmesan cheeses. Toss with 1 tablespoon of cornstarch to prevent clumping.
• In a food processor, combine grated cheese, sun-dried tomatoes, parsley, garlic, and horseradish.
• Add the bread slices, tearing them into smaller pieces if needed. Pulse until the mixture is coarse and moist.
• Adjust consistency: The mixture should stick together when pressed. If it’s too dry, add a touch more horseradish or a few drops of water.

Assemble and Cook the Roast:

• Remove the roast from the fridge and season with black pepper.
• Spread a thin layer of Dijon mustard over the top and sides of the roast using a silicone brush.
• Firmly press about 1 1/2 cups of the breadcrumb mixture onto the mustard-coated surface. Pack it in tightly to ensure it adheres. Reserve leftover breadcrumbs for future use (freeze if desired).
• Lightly spray the crust with canola oil or olive oil spray to help it brown evenly.
• If using the removed bones, place them in a roasting or lasagna pan. Set the roast on top.
• If using the removed bones, place them in a roasting or lasagna pan. Set the roast on top.
• Insert a meat thermometer into the center of the roast. Cover loosely with aluminum foil to prevent the crust from browning too quickly.
• Place the roast in the oven and cook until the internal temperature reaches 118°F–120°F. This will take about 2 1/2 to 3 hours, depending on the size of the roast.
• Remove from the oven and let rest for 30–45 minutes. During this time, juices will be redistributed.

Finish the Roast:

• Increase oven temperature to 500°F (260°C).
• Return the roast to the oven and cook for about 10–15 minutes, or until the crust is golden brown.
• No additional resting is required after this step; the roast is ready to serve immediately.

Enjoy your perfectly cooked horseradish-crusted prime rib!