Cream butter and shortening in a large mixing bowl; add sugar, beating well. Add egg yolks, and beat well.
Combine flour and soda. Add to creamed mixture alternately with buttermilk, beginning and ending with flour mixture. Mix well. Stir in vanilla, coconut, and 1 cup pecans.
Beat egg whites (at room temperature) in a medium mixing bowl until stiff peaks form. Gently fold egg whites into batter. Spoon batter into 3 greased and floured 9-inch round cake pans. Bake at 350° for 25 minutes or until a wooden pick inserted in center comes out clean. Cool in pans 10 minutes; remove layers from pans, and let cool completely.
Spread frosting between layers and on top and sides of cake. Sprinkle additional pecans over top. Slice and serve.