1. Let steak stand at room temperature for 30 min.
2. Preheat oven to 450°. Season steak with salt and pepper to taste.
3. In a cast iron or other heavy oven-safe skillet, heat a small amount of oil or butter (enough to lightly coat the bottom of the pan) over high heat until hot but not smoking.
4. Add steak; cook on one side until a moderately dark crust forms and steak releases easily from the pan. Turn and cook until both sides are seared in this manner.
5. Transfer pan to preheated oven; roast steak to desired doneness as measured with a thermometer.
6. Remove pan from oven. Remove steak from pan; tent loosely with foil and let rest for at least 5 min. before serving (larger steaks can rest longer).
7. While steak rests, follow directions below to make an au poivre or red wine pan sauce, if desired. Spoon or drizzle warm pan sauce over steak just before serving.

AU POIVRE PAN SAUCE: Return pan to stovetop over medium heat; stir 2 tbsp. dry sherry or sherry vinegar into drippings, scraping up browned bits from bottom of pan. Whisk in ⅔ cup heavy cream, ⅔ cup gluten-free beef broth and 1 tbsp. gluten-free Dijon mustard; season generously with freshly cracked black pepper. Cook and stir until sauce is thickened and reduced by ½ (about 5 min.). Season to taste with salt.

RED WINE PAN SAUCE: Return pan to stovetop over medium heat; stir 2 tbsp. dry sherry or sherry vinegar into drippings, scraping up browned bits from bottom of pan. Whisk in ⅔ cup heavy cream, ⅔ cup red wine and 1 tbsp. gluten-free Dijon mustard; cook and stir until sauce is thickened and reduced by ½ (about 5 min.). Season to taste with salt.