Combine the salt, porcini powder, brown sugar, garlic powder and cayenne in a bowl. Use your fingers to make sure the ingredients are evenly distributed. Rub the steaks generously with the rub. Let sit for a few minutes.
Heat a saute pan or cast-iron skillet over high heat until very hot.
Lightly oil the steaks. Working in batches, place one of the steaks in the skillet and get a good sear on both sides, 6 to 7 minutes per side. Add the garlic, 2 sprigs thyme and 2 tablespoons butter to the pan and use a spoon to baste the steak with the butter. Remove the steak to a wire rack set over a baking sheet. Repeat with the remaining steak, thyme and butter.
Add the garlic to the rack with the steaks and roast until the steaks reach the desired doneness, 10 to 15 minutes for medium rare. Let rest in a warm spot for 7 to 8 minutes. Slice on the bias and serve with the roasted garlic.