How to Make It
Heat oven to 400° F. In a large flameproof roasting pan, toss the shallots with 1 tablespoon of the oil and ¼ teaspoon each salt and pepper. Push toward the edges.
Place the pork in the center of the roasting pan and season with 1 teaspoon salt and ½ teaspoon pepper. In a small bowl, combine the mustards, sage, and the remaining 2 tablespoons of oil; spread over the pork.
Roast until the internal temperature of the pork registers 145° F*, 85 to 95 minutes. Transfer the shallots to a platter. Transfer the pork to a cutting board, cover loosely with foil, and let rest for at least 15 minutes before slicing.
Place the empty roasting pan over 2 burners over medium-high heat. Add the wine and simmer, scraping up any browned bits, until thickened, 5 to 6 minutes. Whisk in the sour cream and chives. Serve with the pork and shallots.
*Note: This is the temperature preferred by the Real Simple test kitchen, and it is considered safe by many experts. The U.S. Department of Agriculture’s recommendation for maximum safety is 15° to 20° F higher.