Pressure cookers are a godsend when you need to cook something hearty but you’re short on time. While perhaps you heard a story or two about a pressure cooker blowing up, this usually occurs only due to human error. Electric pressure cookers have safety features, such as lids that lock in place until the pressure dissipates, preventing curious cooks or little helpers from accidentally scalding themselves. They also have high-pressure settings that cook tough cuts of meat, such as the flank steak used in London broil, in about 20 minutes. Since pressure cookers use moist heat instead of dry, they typically turn out more tender London broils than grilling.
Pour 1/2 cup oil and 1/4 cup acid for every pound of flank steak in a saucepan. Classic London broil marinades use vegetable or regular olive oil and a combination of Worcestershire sauce and balsamic vinegar for the base. However, like most rustic dishes that stand the test of time, familial or personal preferences come first.
Add 1 teaspoon of kosher salt for every pound of flank steak along with aromatic ingredients, also known as aromats or aromatics, for short. You can consider anything that adds subtle nuances of flavor and aroma an aromatic, like the carrots, onions and celery used in a soup base. Consider crushed garlic cloves, black peppercorns and shallots for a simple, classic flavor when choosing aromatics for a London broil marinade.
Add 1 tablespoon of fresh spices or 1/3 tablespoon of dried spices to the marinade for every pound of flank steak. Place the saucepan on the stove and set the heat to medium. Heat the marinade for 10 minutes, stirring occasionally with a whisk, and then remove it from the stove. Heat releases the essential oils in herbs, which are only soluble in oil. It also brings out the aromas in aromatic ingredients, similar to making an herb-infused oil. Let the marinade cool to room temperature.
Rinse the flank steak with cool-running water and pat it dry with paper towels. Place the flank steak in a large food storage bag or airtight food storage container.
Pour the marinade over the flank steak and turn it a few times to cover it on all sides. Seal the food storage bag or the lid on the food storage container and place it in the refrigerator. Marinate the flank steak for 2 to 4 hours.
Remove the flank steak from the refrigerator and take it out of the marinade. Let the excess marinade drain from flank steak and place it in the pressure cooker.
Pour 1 to 1 1/2 cup of water, stock or broth for every flank steak in the pressure cooker. If using a natural, sodium-free stock or broth, taste it before adding it and adjust as needed with kosher salt.
Attach the pressure limit valve, sometimes called a regulator, to the pressure cooker and lock the lid in place. Turn the pressure cooker on and program it to cook for 35 minutes.
Release the pressure using your pressure cooker’s quick-release method. Most electric models have a pressure-limiting valve that you pull open, which lets the steam escape. Whether you let the pressure cooker naturally depressurize, which takes about 30 minutes, or use the quick-release method, which takes about a minute, the lid stays locked until it’s safe to open.
Open the pressure cooker when it unlocks. Since the flank steak rested when the cooker depressurized, you can place it on a cutting board and cut it for serving right away. Cut the London broil across the grain at an angle in 1 1/2- to 2-inch-wide strips to make it less chewy.