Season both sides of each steak with the salt and pepper. Heat 1 tbs olive oil in a large heavy skillet over high heat, and place the steaks in the skillet 2 at a time. Cook for 3-4 minutes on each side. Transfer the steaks to a heatproof dish and keep them warm in a 175-degree oven.
Pour any leftover liquid from the skillet and lower the heat to medium. Add the onions and 1 piece of margarine; sauté for 5 minutes, until cooked. Carefully add cognac (it may flame) and bring to a boil for 2-3 minutes until the sauce thickens. Stir in cream; heat throughly, stirring constantly. Serve over steaks immediately.
