Preheat oven to 500º F, ensuring that the intended oven rack is only about 6 inches above the heating element. Pat meat dry with a paper towel and set out at room temperature for 15-20 minutes. During this time, prep ingredients for the mushroom sauce.
Set sauté pan at medium-high heat, then add 1 tablespoon of butter, garlic, shallot, and mushrooms to pan. Sauté until mushrooms are tender (about 5-6 minutes). Add wine and broth, and bring to a boil until only about 2 tablespoons of liquid remains (10-12 minutes). Stir in cream and mustard, and keep warm over low heat until ready to serve.
Sprinkle salt and pepper onto both sides of the meat. Put the skillet on the stovetop at medium-high heat and add the remainder of the butter. When the skillet is hot enough, and the butter is ready (wait until butter starts to bubble, but not too long, or the butter will begin to brown), add the steaks to the skillet. Sear each side for 30 seconds, and then flip and repeat (note: when flipping meat, do not use a fork. This can puncture the meat and result in a dry steak). Be sure to sear all sides of the steak and place the skillet into the oven.
For a medium-rare steak, cook each side for 2 minutes before flipping (rare steak for 1 minute, medium steak for 3 minutes, and well-done steak for 4 minutes). Remove skillet carefully from oven.
Place steaks on serving tray and cover loosely with aluminum foil for at least 5 minutes. If there is liquid remaining in the skillet, take two teaspoons and mix them into the mushroom sauce. Pour sauce over steaks, garnish with parsley, and enjoy!