Lobster stuffed Tenderloin

Place beef tenderloin in a plastic bag set into a shallow dish. Pour salad dressing over tenderloin. Close bag. Marinate in the refrigerator for 8 to 24 hours, turning bag occasionally. Remove meat and tomalley (green liver) from lobster. (If desired, reserve shells for use in stock). Cut lobster into bite-size pieces. In a 10-inch skillet, melt 4 tablespoons of the butter. Add tomalley and cook over low heat for 5 minutes. Add shallots and cook 1 minute more. Stir remaining butter, vermouth and tarragon into the tomalley mixture. Cook and stir over medium heat until liquid is reduced to half. Stir in cream. Continue to cook and stir until thick. Stir in lobster meat. Season with salt and pepper. Set lobster mixture aside. Preheat oven to 500. Drain tenderloin. To butterfly the meat, make a lengthwise cut down the center of the meat, cutting to within 1 inch of the other side and within 1 inch of ends. Spread meat open slightly and spoon in lobster mixture. Fold in the thin end portion. Bring sides of tenderloin together and tie with heavy string at 1 1/2-inch intervals to secure. Place tenderloin on a rack in a shallow roasting pan. Insert a meat thermometer. Roast, uncovered, for 5 minutes. Reduce oven temperature to 350 and roast about 30 minutes for rare (140 ). Let stand 10 to 15 minutes before slicing. Remove string; slice to serve. Makes 8 to 10 servings.