Melt margarine in a small saucepan over medium heat; add pecans, and saute 4 minutes or until browned. Drain pecans, reserving margarine; set margarine aside. Combine pecans and 1 tablespoon flour; stir well, and set aside. Combine reserved margarine, corn syrup, and 1/2 cup brown sugar in a large bowl, beating well at medium speed of an electric mixer. Add egg; beat well. Add egg whites, and beat well. Combine remaining 3 cups flour, baking soda, and salt; add to brown sugar mixture alternately with buttermilk, beginning and ending with flour mixture. Mix after each addition. Stir in pecan mixture and vanilla. Pour batter into a 12-cup Bundt pan coated with cooking spray. Bake at 350 degrees for 45 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 10 minutes; remove from pan. Cool on a wire rack. Combine powdered sugar, 1 tablespoon brown sugar, and skim milk; stir well. Drizzle over cake. calories (25% from fat), 6.9 grams fat (1.1 g sat, 3.4 g mono, 1.9 g poly), 14 mg cholesterol and 174 mg