20-30 minutes before you start cooking, remove the steaks from the refrigerator and let sit at room temperature.
Preheat your grill to high. Season steaks liberally with salt and pepper on both sides.
Place steaks on grill over direct heat. Cook approximately 4-5 minutes, until a golden-brown char has developed. Flip and cook another 3-5 minutes, until internal temperature reaches 135 degrees F for medium-rare.
Remove steaks to a large platter, and tent with aluminum foil. Allow to rest while preparing the mushrooms.
Heat the olive oil and 1 tablespoon butter in a large skillet. Add the mushrooms and season with kosher salt. Cook mushrooms over medium-high heat for approximately 6-8 minutes, until they just begin to brown. Stir in shallots, and cook another 2 minutes. Add garlic, and stir for 30 seconds.
Add sherry carefully, to avoid any possible flare-ups. Stir about 1 minute, until mushrooms are coated and sherry is almost evaporated.
Stir any juices from the steak platter into the pan. Add the remaining butter and thyme. Slice the steaks, top with mushroom mixture, and enjoy!