Season filets with salt and pepper; dust lightly with flour. Heat butter in large skillet over medium-high heat. Add filets; cook about 4 minutes on each side or until browned. Remove beef filets.
Holding pan away from heat, add Marsala and red wine. Return back to stove top; cook over medium-high heat until reduced by half. Add stock, fennel and tomato paste. Simmer until reduced by half; season with salt and pepper to taste.
Return filets to skillet and cook in sauce 3 to 5 minutes over medium-high heat for a medium degree of doneness. Place filets on warm serving plates and spoon sauce over each filet.