Preheat oven to 375 degrees F. Trim fat from steaks. Sprinkle steaks all over with pepper and 1/2 teaspoon of the salt. In an extra-large skillet heat butter over medium heat. Brown steaks in butter, turning once. Transfer steaks to a rack set in a shallow roasting pan. Reserve drippings in skillet.
Roast, uncovered, until desired doneness. Allow about 20 minutes for medium-rare (145 degrees F) or 25 minutes for medium (160 degrees F). Cover steaks with foil; let stand 5 minutes.
Meanwhile, in a bowl combine boiling water and porcini mushrooms. Cover and let stand 10 minutes. Strain mushrooms though a fine-mesh sieve, reserving liquid. Rinse mushrooms well with cold water; drain Chop mushrooms.
In the same skillet cook cremini mushrooms, the shallot, and garlic in pan drippings over medium heat 6 to 8 minutes or until mushrooms are tender and lightly browned, stirring occasionally. Carefully add the mushroom soaking liquid. Bring to boiling, scraping up any browned bits on bottom of the pan. Simmer until reduced by half. Add cream, chopped porcini mushrooms, dried thyme (if using), and the remaining 1/4 teaspoon salt. Bring to boiling; reduce heat. Simmer, uncovered, 8 to 12 minutes or until slightly thickened. Stir in fresh thyme (if using).
Spoon mushroom sauce over steaks. If desired, sprinkle with blue cheese.