Sirloin steak and its neighbor, top sirloin, are two of the most tender cuts of beef in the geography of a cow. Tucked behind the rib cage, the sirloin is a hunk of beef that doesn't do much. There's little marbling, it doesn't show much connective tissue and the muscle is lightly used. The London broil, in reality, isn't a cut of beef at all, but rather a style of preparing a piece of beef round.
Tender Is the Steak
Tenderness in a piece of beef is created by veins of fat running through it. Not the chunks of fat that are tucked into a grocery store's package of beef and added to the weight and cost, but thin strands permeating the beef from end to end. That fat is what creates the flavor in a steak.
And while we're on the subject of fat, let's dispel a few myths about beef, the fat it contains and diet. Sirloin and round cuts are lean, and the American Institute for Cancer Research recommends eating no more than 18 ounces of lean, red meat a week. That's three 6-ounce steaks a week. Since they are packed with protein, the lean meats fill you up faster, meaning you need to eat less in order to feel full. And lean, grass-fed beef is the better choice because of the reduced fat and antioxidants it contains.
Given a choice of a sirloin and a top sirloin, go for the top sirloin. It's the cut that's nearest the tenderloin and reflects its tender anatomical heritage. The marginal price difference between the sirloin and top sirloin cuts mean a more tender steak with more flavor. The top sirloin is also a leaner cut than the sirloin.
London broil, or top round, is a muscular piece of meat cut from the rear of the cow. Not from the expensive loin section and not large enough to be considered a roast, the top round is lean but tough, which is why preparing it properly is important to the enjoyment of the cut. In truth, any cut of round or flank steak can be used as a London broil as long as it's well marinated and sliced thinly.
Dressing the Steaks
Because the round, or London broil cut is muscular and lean, acids are needed to penetrate the beef to tenderize it. Low sodium soy sauce or teriyaki sauce with grated ginger enhances the flavor and adds dimension. Throw in a little minced garlic and some honey and let the meat swim, turning it to cover both sides. Lemon juice or vinegar are also acids, but use them in moderation. Don't overwhelm the meat.
A lengthy marinating session toughens the proteins in the beef. Limit the marinating process to a short 20 to 30 minutes to give the round great flavor as well as to create the tenderness needed.
A sirloin doesn't need much enhancement prior to cooking. A bit of salt and pepper on the dry steak is all that's required. Be sure the steak is room temperature before heating.
Into the Pan
Broiling or grilling a sirloin is the best way to chase all the flavor out of it. A sirloin needs slow heat, a heat that won't shrink the steak. The work is in keeping the juices inside the beef, not wasting them on the bottom of the pan.
Reverse searing is an ideal way to prepare the sirloin. Season it, put it into an oven preheated to 275 degrees Fahrenheit and let it just sit there for about 40 minutes. When the internal temperature reaches 125 F, take the steak out, cover it with foil and continue its rest for another 15 minutes.
The final step is to preheat a skillet on high and spread a tiny bit of vegetable oil on the surface. Sear the sirloin for 1 minute on each side before removing it. Let it rest again for a few minutes before slicing into 1/2-inch strips. The juice will come tumbling out and is perfect for spooning over the luscious piece of beef prior to serving.
The London broil, because of its toughness, also needs a slow preparation unless you're thinking of shredding it. Again, slow roast it in a 275 F oven until the glaze is caramelized and the internal temperature reaches 125 F. After sitting for a few minutes, sear both sides for a minute each. Slice very thin strips against the grain and spoon any dripping marinade over the steak. The flavor shouldn't be overwhelmed by the marinade, and diners will appreciate the large beef flavor.
A salad bursting with fresh ingredients along with a serving of fresh vegetables, or a salad topped with slices of sirloin or round are two very diet-conscious ways to enjoy both a sirloin and a London Broil.