Pat the cubed steak dry
Season both sides with salt and pepper
Dredge in flour if desired
Heat oil or butter in a skillet over medium-high heat
Sear the steak for 2 to 4 minutes per side
Reduce heat to medium-low
Add sliced onions or gravy ingredients if desired
Cover and cook until tender, about 20 to 30 minutes
Flip once or twice while simmering
Check that the internal temperature reaches 145°F for medium-rare or higher to taste
Rest for 5 minutes before serving