Grease and lightly flour 2 9-inch round cake pans. In a mixer bowl combine the flour, sugar, baking powder, baking soda, and salt. Add shortening and banana; beat at low speed until combined. Add buttermilk or sour milk, eggs, and vanilla. Beat 2 minutes at medium speed. Turn batter into pans. Bake at 350 for 30 minutes or until cake tests done. Cool 10 minutes in pans. Remove from pans and cool on wire racks.