Step 1Cream butter and shortening with sugar on medium speed until fluffy. Add eggs, then vanilla, Kahlua and mashed bananas, scraping down often to blend batter evenly. (If mixture is very curdled in appearance, stir in 1 cup of flour from recipe).
Step 2Mix together flour, baking powder, baking soda and salt, and fold into batter. Fold in walnuts. Spoon into generously greased 13-by-9-inch baking pan. Bake at 350 degrees until toothpick inserted in center comes out clean, 45 to 55 minutes. Cool 10 minutes before removing from pan. Drizzle with Espresso Cream Cheese Drip Glaze or garnish with powdered sugar.
Step 1Cream cream cheese with butter. Stir in instant espresso and powdered sugar, and blend well to make soft glaze. Thin with water, if necessary, to achieve a just-pourable glaze. Drizzle or spread onto cooled cake. Garnish with chopped walnuts.