Preheat oven to 350 degrees F. Spray two 8-inch square or round cake pans with vegetable oil spray. For cake, in a medium bowl, stir together flour, baking powder, cinnamon, and baking soda. In a large mixing bowl, beat brown sugar and margarine with an electric mixer on medium until well blended. Add buttermilk, egg whites, and vanilla; beat on medium until well blended. Gradually add flour mixture to buttermilk mixture, beating on low after each addition just until blended. Fold in carrots and raisins. Divide batter evenly between two cake pans. Bake for 20 to 25 minutes, or until a toothpick inserted in center comes out clean. Let stand on cooling racks for 10 minutes. Invert cakes onto racks, remove pans, and let cool completely. Meanwhile, in a medium mixing bowl, combine icing ingredients except confectioners’ sugar. Beat on low just until smooth (don’t overbeat or icing will be too thin). Gradually add 3 cups confectioners’ sugar, beating on low until thick; add more confectioners’ sugar if necessary to reach icinglike consistency. Transfer mixture to a shallow bowl, cover with plastic wrap, and refrigerate until thick and spreadable, about 1 hour. To assemble, place one cake layer on a serving plate; spread ½ cup icing over top of cake only. Place a second cake layer on first and spread remaining icing over top and sides. Cover loosely with plastic wrap and refrigerate until ready to serve. |