Pat steak(s) dry with paper towels, and place in a shallow dish. Drizzle with oil; rub oil all over steak(s). Generously season both sides with kosher salt and freshly ground black pepper, to taste (rubbing seasonings into meat with your fingers). Let stand at room temperature for at least 30 minutes, and up to an hour.

Place a 10- to 12-inch cast iron skillet(s) on an oven rack adjusted to lower-middle position, and heat oven to 500 degrees F. When oven has reached temperature (about 15-20 minutes), remove skillet(s) from oven (do not turn oven off) and quickly transfer to stove top burner(s) over high heat (be careful--skillet and handle will be extremely hot).

Immediately place steak(s) in middle of hot, dry skillet(s). Sear steak(s) for about 1-2 minute without moving. Flip with tongs and sear second side for another 1-2 minute without moving, or until both sides are well browned and a nice crust has formed. Quickly remove skillet(s) from stove top and place back into oven, and cook until done to your preference. Cook for about 2-3 minutes on each each side for a medium-rare steak(s), or about 3-4 minutes on each side for a medium steak(s). Remember that meat will continue to cook from residual heat when removed from oven, so remove steak(s) from oven when slightly less done than you wish.

When steak(s) is done to your liking, transfer to a plate(s). Double check doneness by thermometer (rare - 130 to 140 degrees F; medium-rare - 140 to 150 degrees F; medium - 150 to 160 degrees F; medium-well - 160 to 170 degrees F), or by touch. (rare is soft to the touch; medium-rare yields gently to the touch; medium yields only slightly to the touch and is beginning to firm up; medium-well is firm to the touch). Tent steak(s) loosely with foil and let rest for about 5 minutes to allow the meat juices to redistribute and settle before serving. Serve as individual steak(s) or slice just before serving on warmed plate(s).

Red Wine-Mustard Pan Sauce (optional):

After pan-searing, remove meat from pan leaving fond (brown bits in pan leftover from cooking) and residual fat that it was cooked in. Add shallots to pan and cook over low heat , stirring frequently until shallots are translucent.

Raise heat to high, add wine, stock, and bring to a boil. Using a wooden spoon or spatula, stir mixture, scraping to loosen any flavorful browned bits stuck to pan and incorporate them into sauce. Boil until liquid is reduced by half.

Reduce heat to medium, add balsamic vinegar, Dijon mjustard, and cook until reaching sauce consistency you desire. It should be thick enough to coat back of a regular spoon.

Remove from heat, whisk in butter until melted and sauce is thickened, smooth, and glossy. Add fresh thyme, season with salt and pepper to taste. Spoon sauce over cooked steaks and serve immediately.

Food Safety Note:

Doneness is an issue of personal preference. However, it is recommended that beef be cooked to medium-rare doneness, the internal temperature should reach a minimum of 145 degrees F to ensure that harmful bacteria have been destroyed. A thick steak that has been cooked to an internal temperature of 140 degrees F, may be removed from the oven, loosely cover, and allowed to rest a few minutes. The temperature will continue to rise about 5 degrees F, reaching the proper doneness.