Cream butter and Shortening thoroughly; add sugar, 1/2 cup at a time. Beat until light. Add eggs, one at a time, beating after each addition. Add 2 cups flour alternately with milk containing flavoring. Add the last 1 cup flour containing salt and baking powder. Stir in 1 cup finely chopped walnuts. The batter will be thick and fluffy. Spoon into tube pan, which has been lightly greased and floured. Place the cake in cold oven on middle shelf. Turn oven to 350 degrees. Don't open door for 1 1/4 hours. Allow cake to cool in pan on wire rack