Cream butter and shortening. Add 2 cups sugar, beat until fluffy. Add eggs, one at a time, beating well after each. Combine milk and vanilla, set aside. Sift together flour, baking powder and salt. Add milk mixture and dry mixture alternately to creamed mixture, beating just enough to keep batter smooth. Combine cinnamon and remaining sugar, sprinkle 1 ½ tsp into a greased 10 in. tube pan. Pour 1/3 of batter into pan, sprinkle with ½ of remaining cinnamon-sugar, top with 1/3 of batter, repeat layers, smooth with spatula. Bake at 350 for 1 hour and 15 minutes. Cool for 10 minutes, remove from pan to finish cooling.