1Boil stock in small saucepan until reduced to 3/4 cup, about 7 minutes.
2Meanwhile, melt butter in large skillet over medium-high heat. Season steaks with salt and pepper. Cook steaks to desired doneness, about 4 minutes per side for medium-rare. Transfer steaks to plate (do not clean skillet).
3Add chopped shallots to same skillet and saute 2 minutes. Remove from heat. Add reduced beef stock, 1 cup whipping cream, 3 tablespoons Cognac and green peppercorns. Boil until mixture thickens to sauce consistency, about 6 minutes.
4Season sauce to taste with pepper. Spoon sauce over steaks and serve.