Cream butter; add sugar, beating well. Add eggs, one at a time, beating well after each addition. Combine next 3 ingredients; add to creamed mixture, beat well. Dissolve soda in buttermilk, stirring well. Combine flour and salt; add to creamed mixture alternately with buttermilk mixture, beginning and ending with flour mixture. Pour batter into 2 greased and floured 8-inch round cakepans. Bake at 325 for 35 minutes. Cool in pans 10 minutes; remove from pan, let cool completely. Spread frosting of choice between layers and on top of cake.