Preheat oven to 350 degrees. Grease and flour three 8x4 inch loafpans.
Beat butter and cream cheese at medium speed with an electric mixer until creamy. Gradually add sugar, beating until light and fluffy. Add eggs, 1 at a time, beating just until blended after each addition. Add vanilla.
Combine flour, baking powder, baking soda, and salt in separate bowl. Gradually add to butter mixture, alternating with mashed bananas. Beat at low speed after each addition just until blended. Stir in walnuts. Spoon batter into prepared pans.
Bake in preheated oven for 50 minutes or until a long wooden pick inserted in center comes out clean, top is golden brown, and sides pull away from pan. If necessary, shield with aluminum foil last 15 minutes to prevent browning.
Cool bread in pans on wire racks for 10 minutes. Remove from pans and cool 30 minutes on wire racks before slicing.
Prepare browned butter icing while bread cools. Heat butter in a saucepan over low heat until golden brown, about 15 minutes. Remove from heat and stir in confectioners' sugar, cream, and vanilla extract. Add water, mixing vigorously until smooth.
Drizzle browned butter icing over bread before serving.