Sprinkle beef evenly with salt and freshly ground pepper.
Melt 2 tablespoons butter with oil in a large skillet over medium-high heat; add steaks, and cook 8 minutes. Turn and cook 5 more minutes or to desired degree of doneness. Remove steaks from skillet, reserving drippings in pan. Keep steaks warm.
Melt remaining 2 tablespoons butter in skillet over medium-high heat; add mushrooms, and sauté 3 to 4 minutes. Remove mushrooms from skillet.
Add sherry and cream to skillet; cook, stirring constantly, over high heat 1 to 2 minutes or until thickened. Stir in mushrooms. Serve mixture over beef; garnish, if desired.