Preheat oven to 350 degrees. Grease and flour or spray three 8" round cake pans using a baking spray with flour. In medium bowl, combine and sift cake flour, baking soda and baking powder. Melt white chocolate in hot water. Cool. In small mixing bowl, beat egg whites until stiff peaks form; set aside. In large mixing bowl, cream butter, sugar and vanilla. Beat in egg yolks one at a time. Add melted chocolate. Add buttermilk alternately with dry ingredients. Fold in egg whites. Stir in nuts, coconut and (cherries, optional). Bake for 25-30 minutes or until toothpick inserted in centers comes out clean. Cool in pans on wire rack for 10 minutes. Remove from pans and cool completely.
White Chocolate Frosting: In medium saucepan, with a wire whisk ,mix flour and half & half until smooth; add white chocolate. Over medium heat, cook stirring constantly until mixture is very thick about 5-10 minutes. Cool completely. In large mixing bowl, cream butter, sugar and vanilla. Beat about 3 minutes or until mixture is light and fluffy. Gradually add (completely cooled) white chocolate mixture. Beat at high speed until it is the consistency of whipped cream. Spread frosting between layers, on top and sides of cake. If desired, sprinkle cake with coconut.