How to Make It
Preheat oven to 350°.
Coat a 12-cup Bundt pan with cooking spray; dust with breadcrumbs.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking soda, and salt, stirring well with a whisk. Place sugar and butter in a large bowl; beat with a mixer at medium speed until light and fluffy (about 3 minutes). Add rind, juice, and extract, beating until well blended. Add egg whites and egg, 1 at a time, beating well after each addition. Add flour mixture to sugar mixture alternately with sour cream, beginning and ending with flour mixture. Stir in walnuts.
Spoon batter into prepared pan. Bake at 350° for 50 minutes or until a wooden pick inserted in center comes out clean. Cool in pan 15 minutes on a wire rack; remove from pan. Cool completely on wire rack. Sprinkle with powdered sugar.