Generously season the roast with kosher salt and place in the refrigerator, uncovered, for 1 hour. Then, remove prime rib from refrigerator.
Kosher salt, 5-6 pound prime rib roast
Place the roast in a large vacuum bag, and seal it tightly.
Set sous vide machine to 132-degrees (for medium-rare) and attach it to a large pot filled with water. Place sealed roast in the water bath. Clip the bag to the side of the pot to ensure it stays submerged. Sous vide for 6 to 10 hours.
Remove the beef from the bag once the cooking time is up. Reserve the cooking liquid! Pat the roast dry. Preheat oven to 550°F. In the meantime, in a small bowl, combine butter with garlic powder, rosemary, thyme, and pepper. Coat the top and sides of the roast with the garlic herb butter.
1 stick salted butter, 2 Tablespoons garlic powder, 1 Tablespoon fresh rosemary, 1 Tablespoon coarse ground black pepper, 1 Tablespoon fresh thyme
Place in a roasting pan with a rack. Roast the prime rib for 8-10 minutes, until the crust is golden (keep a close eye on it!).
Remove from the oven and let rest. While the roast rests, make the au jus. In a large skillet, bring the sous vide cooking liquid and beef broth to a boil.
1 quart low-sodium beef broth
Reduce the heat and simmer until reduced by half. Skim off any solids that rise to the top.
Whisk sour cream, horseradish, Dijon mustard, champagne vinegar, Worcestershire sauce, chives, salt, pepper, and tabasco sauce in a medium size bowl to make your horseradish sauce.
¼ cup prepared horseradish, 1½ Tablespoons dijon mustard, 1 teaspoon champagne vinegar, 1 teaspoon Worcestershire sauce, ½ Tablespoon fresh chopped chives, salt and pepper to taste, a few drops Tabasco sauce, 1 cup sour cream
Serve sliced prime rib and serve with creamy horseradish sauce and Au Ju on the side.