1 tablespoon vegetable oil
1 boneless shell sirloin steak (top butt) or whole flap meat steak, about 1 pound and 1¼-inches thick
1 small shallot, minced (about 2 tablespoons)
1½ tablespoons dry white wine
¼ cup low-sodium chicken broth
3 tablespoons heavy cream
1½ tablespoons whole-grain Dijon mustard or coarse brown mustard
Cook’s Illustrated has a wonderful primer on steaks and mentions that this type of steak is also known as boneless shell sirloin, butt steak, top sirloin butt, top sirloin steak and center-cut roast. Additionally, the flap meat steak can also be found as top sirloin tips, beef sirloin tips, sirloin tip steak and sirloin flap meat for tips. Just remember to keep an eye out for various names since they can vary by region and market.
Heat oil in a large skillet over medium-high heat. Season both sides of the steak with salt and pepper, then place in skillet. Cook, without moving, until well browned, about 2 minutes. Using tongs, flip steak. Reduce heat to medium and continue cooking until well browned on the second side. For medium-rare, cook for about 5 minutes or until the internal temperature reaches 125º. For medium, cook for about 6 minutes or until steak reaches 130º.
Remove steak from skillet and place on a large plate or cutting board. Tent loosely with foil and allow to rest until the temperature reaches 130º for medium-rare and 135º for medium, anywhere from 12 to 15 minutes.
Meanwhile, pour off all but 1 tablespoon of fat from the skillet. Return to low heat and add shallot. Cook, stirring frequently, until the shallot begins to brown, 2 to 3 minutes. Add wine and increase heat to medium-high. Simmer rapidly for about 30 seconds and use a wooden spoon to scrape up any browned bits that may have formed on the bottom of the skillet.
Add broth and simmer until reduced to 2 tablespoons, about 3 minutes. Add cream and any juices from the resting steak. Continue cooking for about a minute, then stir in mustard. Season to taste with salt and pepper.
Using a sharp knife, slice steak about ¼-inch thick against the grain on the bias. Arrange on two plates, spoon sauce over the top and serve immediately.