Heat a 12-inch cast-iron skillet over high heat until very hot, about 3 minutes. Meanwhile, thoroughly pat the steaks dry with paper towels. Lightly coat each side of the steaks with canola oil and sprinkle generously with salt and pepper.
Add 1 to 2 tablespoons canola oil to the skillet (this will help create a great crust on the steaks) and add the steaks. Do not crowd them; if you cannot leave room between the steaks, use 2 skillets. Without moving them, cook the steaks 3 minutes. Using tongs, flip them and cook 1 more minute for rare, 2 more minutes for medium rare or 4 more minutes for medium. Transfer the steaks to a plate and cover loosely with foil. Let rest at least 5 minutes before cutting into them.
Pour out the used oil from the skillet and add a glug of new oil. Reduce the heat to medium. Add the shallots and garlic to the skillet and cook until they just begin to brown, 3 to 5 minutes. Add the beef broth, Worcestershire sauce and sherry vinegar and bring the sauce to a boil. Cook until reduced by half, 3 to 5 minutes. Turn off the heat and whisk in the butter until it has melted and the sauce has thickened. Stir in the olives, if using.
Put each steak on a plate; spoon the sauce over the top and sprinkle with chives.