Prime Rib with Mustard Cream Sauce

To cut the meat off the bone (see note 1):

1. Hold the meaty lobe in one hand and a sharp boning or chef's knife in the other hand, run knife down length of first bone, following contours as closely as possible to separate it from meat.
2. Flip roast so uncut portion faces you. Holding bones back with your hand, cut meat from remaining ribs. Once meat is removed, proceed with seasoning and tying as directed in recipe.

To make the prime rib:

1. Using sharp knife, cut slits in surface layer of fat, spaced 1 inch apart, in crosshatch pattern, being careful not to cut into meat. Rub 2 tablespoons Kosher salt over entire roast and into slits. 
2. Place meat back on bones (to save space in refrigerator), transfer to large plate, and refrigerate, uncovered, at least 24 hours and up to 96 hours. 
3. Adjust oven rack to middle position and heat oven to 200 degrees. Heat oil in large skillet over high heat until just smoking. Sear sides and top of roast (reserving bone) until browned, 6 to 8 minutes total (do not sear side where roast was cut from bone).
4. Place meat back on ribs, so bones fit where they were cut, and let cool for 10 minutes. Tie meat to bones with 2 lengths of kitchen twine between ribs. Transfer roast, fat side up, to wire rack set in rimmed baking sheet and season with pepper (or to a roasting pan with a rack set inside). Roast until meat registers 110 degrees, 3 to 4 hours. 
5. Turn off oven, leave roast in oven, opening door as little as possible, until meat registers about 120 degrees (for rare) or about 135 degrees (for medium-rare) 30 minutes to 1 1/4 hours longer. 
6. Remove roast from oven (leave roast on baking sheet), tent loosely with aluminum foil, and let rest for at least 30 minutes or up to 1 1/4 hours. 
7. Adjust oven rack about 8 inches from broiler element and heat broiler. Remove foil from roast, form into 3-inch ball, and place under ribs to elevate fat cap. Broil until top of roast is well browned and crisp, 2 to 8 minutes.
8. Transfer roast to carving board. Slice meat into 3/4-inch thick slices. Season to taste with salt.

To make the mustard cream sauce:

1. In a small saucepan over medium heat, whisk together sour cream, heavy cream, yolks, mustard, vinegar, sugar, and 1/2 teaspoon salt. Cook, whisking constantly, until sauce thickens and coats back of spoon, 4 to 5 minutes. 
2. Immediately transfer to serving bowl, stir in chives, and season with salt and pepper to taste. Serve warm or at room temperature. Makes about 3 cups.