Standing Roast Rib of Beef with Potato Rosti

PREPARE BEEF:

Preheat the oven to 350F.

Season the beef generously with salt and pepper.

Place a large roasting pan over medium-high heat.

Add the oil to the pan and cook the beef just until brown on all sides, about 8 minutes.

Remove the pan from the heat.

Set the beef on a platter.

PREPARE ROAST:

Add the carrots, celery, shallots, and thyme to the pan and stir to scrape up any brown bits on the bottom of the pan.

Arrange the vegetables and thyme in the center of the pan and set the beef on top of the vegetables and thyme.

Roast the beef and vegetables in the oven until an instant-read meat thermometer inserted into the center of the beef registers 125F, basting once or twice with the pan drippings, about 1 hour and 45 minutes to 2 hours.

Transfer the beef to a cutting board and allow it to rest tented with foil for 30 minutes.

Add the stock to the vegetables in the hot pan and stir to scrape up any brown bits on the bottom of the pan.

Strain the jus through a fine-meshed strainer and into a saucepan. Discard the solids.

Freeze the jus then spoon off the fat that rises to the top of the jus.

Re-warm the jus over low heat before serving.

Reduce the oven temperature to 200F.

PREPARE THE POTATOES:

Using a mandolin, cut the potatoes lengthwise into thin strips that resemble linguine.

Toss the potatoes in a large bowl with the onions and salt. Set aside for 5 minutes to allow the potatoes to exude their liquid.

Place the potatoes in the center of a clean large tea towel or cloth.

Fold the towel up around potatoes and twist to squeeze out all of the liquid.

Toss the potatoes in a clean dry bowl with the thyme leaves.

COOK THE POTATOES:

Place a large nonstick saute pan or flat griddle pan over medium heat until the pan is hot.

Drizzle 1 tablespoon of oil in the pan. Place the potato mixture into the pan forming 3 patties and press the potatoes with a spoon to compact them. Drizzle 2 teaspoons of oil over the potatoes.

Cook for 5 minutes or until the potatoes are crisp and golden brown on the bottom.

Using a metal spatula to help, turn the potatoes over in the pan and continue to cook 5 minutes longer, or until they are golden on the bottom and the potatoes are tender throughout.

Transfer the rosti to a plate lined with paper towels to soak up the excess oil, then place them on a baking sheet and keep them warm in the oven.

Repeat with the remaining potatoes to form 6 rosti potatoes total.

TO SERVE:

Whip the cream in medium bowl until thick but not stiff.

Fold the horseradish and mustard into the cream. Season to taste with salt and pepper.

Cut the beef into slices and serve alongside the rosti potatoes.

Spoon some of the warm jus over the beef and serve the horseradish sauce alongside.