Banana-Walnut Cake
["1 stick butter, softened", "1 1/3 c. granulated sugar", "3 large eggs", "1 tsp. vanilla", "3 medium, very ripe bananas, mashed (1 c.)", "2 c. unsifted all-purpose flour", "1 1/2 tsp. baking powder", "1 tsp. baking soda", "1/4 tsp. salt", "1/2 c. buttermilk", "3/4 c. toasted chopped walnuts", "1 ripe banana, thinly sliced (garnish)"]
["Preheat oven to 350\u00b0. Grease and flour two 9-inch round cake pans. In a bowl, beat together at medium speed butter and sugar until fluffy. Beat in eggs, one at a time, then beat in remaining ingredients (except walnuts) in order listed. Mix until well blended. Stir in 1/2 cup walnuts. Spread in prepared pans. Bake at 25 minutes or until wooden pick inserted in centers comes out clean. Cool in pans on racks for 10 minutes. Invert. Cool completely on racks."]
["butter", "sugar", "eggs", "vanilla", "bananas", "flour", "baking powder", "baking soda", "salt", "buttermilk", "walnuts", "banana"]