Make ahead: cube the steak and mix the sauce (without the butter) up to 2 days ahead. Swap soy sauce for tamari to make it gluten-free, or swap butter for olive oil to make it dairy-free. Leftovers keep in the fridge for 3-4 days — reheat in a hot skillet with a splash of broth, not the microwave, so the caramelized crust stays intact.