Cream butter and shortening. Add sugar and beat until very light. Add flavouring and beat again. Add flour mixed with baking powder, alternating with milk, starting and ending with flour. Fold in walnuts.
Pour into a tube pan that has been greased and floured. Use one very large pan, size 4 3/4 x 9 inches and bake for 80 minutes. Or use two regular pans, size 3 1/2 x 9 inches and bake for 70 minutes. Bake at 325 degrees. Do not open oven door during the first hour.