Rub both sides of the steak with 1/2 tablespoon oil, and sprinkle with the salt and pepper. Stir together the espresso granules and ancho chile powder in a small bowl. Rub both sides of the steak with the espresso mixture, pressing to adhere. Let stand at room temperature for about 30 minutes.
Place a large cast-iron skillet in the preheated oven until hot, about 10 minutes.
Remove the hot skillet from the oven; add the remaining 1 tablespoon oil and place over high heat on the stovetop. Add the steak to the skillet and cook, undisturbed, until a crust has formed, 2 1/2 to 3 minutes. Flip the steak and cook, undisturbed, for another 2 1/2 to 3 minutes. Using tongs, hold the steak upright to brown the edges and cook, turning occasionally, until the edges are browned, about 6 minutes.
Return the skillet to the oven and bake until a meat thermometer inserted in the thickest portion registers 145 degrees F, 6 to 8 minutes for medium-rare, or to the desired degree of doneness. Remove the steak from the skillet; top with the butter and let rest for about 10 minutes before slicing.