Beef Tenderloin With Shallot Mustard Sauce

Heat oven to 425 degrees. Coat beef on all sides with the salt and pepper. Place a skillet with an ovenproof handle over medium-high heat, and add olive oil. When very hot, add meat; sear on all sides until browned. Transfer the pan to oven for 10 minutes. Add shallots to pan; return to oven for 15 to 20 minutes more, or until a meat thermometer registers 135 degrees for medium rare. Remove beef from pan; let rest on a cutting board for at least 10 minutes.

Place the pan with the shallots over medium-high heat, and deglaze by adding balsamic vinegar, stirring up any browned bits from the bottom with a wooden spoon. Add the stock, and simmer until slightly reduced, 2 to 3 minutes. Reduce heat to low, and stir in mustards and butter. Keep sauce warm until serving. Cut beef into 1/2-inch-thick slices; top with the sauce, and serve.