Instructions

1. Preheat oven to 325 degrees.
2. If time allows, let steaks rest at room temperature 1 hour before cooking. Line a baking sheet with parchment or foil. Rub both sides of steaks with cut side of garlic. Liberally season both sides of beef with kosher salt and freshly ground pepper. Heat oil in a heavy-bottomed skillet until hot but not smoking. Add steaks to the skillet and sear on one side for 2-3 minutes, or until a crust forms. Flip steaks, add butter to pan, and sear an additional 2-3 minutes. Do not jiggle or move pan while searing so steaks may develop a crust.
3. Remove seared steaks from pan, reserving 2 tablespoons pan juices, then turn off heat on stove. Place seared steaks on baking sheet, on middle rack of oven, five to twenty minutes or until steaks are cooked to the desired level of doneness, 120-130 degrees for rare to medium rare. Remove steaks from oven and tent with foil.
4. While steaks are in oven, make sauce by sautéing mushrooms until just limp in pan juices. Remove and reserve. Add shallots and garlic to the reserved pan juices in skillet and sauté, stirring over medium heat, for 1 minute. Stir one cup of the wine and the stock into the pan. Over medium-high heat, reduce liquids to approximately 1 1/2 cups.
5. Combine the cornstarch with the 2 remaining tablespoons of wine. Whisk the cornstarch-wine mixture, and rosemary into the reduced pan liquid and simmer for several minutes, whisking the sauce until it thickens. Add kosher salt and freshly ground pepper to taste, if needed, and additional butter for added richness &/or sugar, if desired. Return mushrooms into the pan and heat through.
6. Spoon the sauce over the steaks, drizzle with truffle oil, if using, and garnish with rosemary sprigs if desired.