Place the ribeye steaks on a rack and transfer to the fridge, uncovered for at least an hour. This helps the steaks get that golden brown sear on the outside.
Using a coffee grinder, grind the porcini mushrooms until it is the consistency of powder. Coat both sides of the ribeye with 1 teaspoon of the mushroom powder.
Season liberally with kosher salt and black pepper. Using your fingers, press the seasonings into the steak.
Heat a cast iron skillet over medium high heat. When it is very hot, add olive oil. Swirl the pan so it is evenly coated. Gently lay the steaks into the pan and sear on each side for 3 minutes, until a golden brown crust has formed. Then, continue flipping the steak one minute at a time, until a deep brown crust has formed and the temperature reaches 120-130 degrees, about 5 minutes total. Transfer steak to a cutting board and let rest for 5 minutes before slicing into 4 large chunks.