Preheat oven to 350°. Beat butter and shortening at medium speed with an electric mixer until fluffy; gradually add granulated sugar, beating well. Add egg yolks, 1 at a time, beating until blended after each addition. Add vanilla extract, beating until blended.
Combine flour and soda; add to butter mixture alternately with buttermilk, beginning and ending with flour mixture. Beat at low speed until blended after each addition.
Beat egg whites until stiff peaks form; fold into batter. Pour batter into 3 greased and floured 9-inch round cakepans.
Bake at 350° for 25 minutes or until a wooden pick inserted in center comes out clean. Cool in pans on wire racks 10 minutes; remove from pans, and cool completely on wire racks. Brush cake layers evenly with liqueur. Spread half of Butterscotch Filling between each cake layer; spread Cream Cheese Frosting on top and sides of cake. Gently press chopped pecans onto sides of cake; arrange pecan halves on top.