Heat the Instant Pot insert on the sauté setting and add the 1 tablespoon of avocado oil.
Add the London broil and brown on each side until a crust forms, about 1 minute per side. Turn the sauté setting off.
Add the remaining ingredients (except mushrooms, salt and remaining avocado oil).
Pressure cook on high for 3 minutes. Let the pressure release naturally for 7 minutes, then release any remaining pressure.
While the meat cooks, heat a skillet over medium heat and add the oil.
Add the mushrooms and salt and cook, stirring regularly, until mushrooms are browned and have released their liquid (softened).
Remove the London broil from the instant pot and let rest for 10 minutes.
Turn the Instant Pot to the sauté setting and simmer the sauce. Thicken with a cornstarch slurry if desired (1 tablespoon cornstarch mixed with 1 tablespoon water and added to the liquid while whisking).
Slice the London broil and serve with the sautéed mushrooms and cooking liquid.
Notes
Make sure you brown the London broil first before pressure cooking as this will add flavor and seal in the juices.
When browning the London broil just do so for 1 minute per side. If you over cook it, you may end up with a tough steak.
Don’t leave out the wine or soy sauce. Not only are they added for flavor, but they’re the required liquid to help bring the Instant Pot to pressure.
Make sure you naturally release the pressure for 7 minutes as the London broil will continue cooking during this time.
While this London broil recipe takes just 3 minutes to cook on high pressure in the Instant Pot, you’ll need to factor in time for pressure to build and release.
For more flavorful results, salt the London broil and let it sit in the fridge, uncovered, overnight before cooking.
Let your London broil rest for 10 minutes before slicing it. This will allow time for the juices to redistribute throughout the steak.