Break up candy bars and melt in hot water on top of double boiler; cool. Cream butter and sugar well. Beat in egg yolks beating well, then add sour cream and beat well. Blend in cooled candy bar-water mix and vanilla. Stir in flour ( do not beat!) until blended, then add baking soda which has been dissolved in 3 tb water. Gently fold in egg whites which have been stifly beaten with the salt. Bake in 2 lightly buttered and floured 9" round layer pans in preheated 350~F oven for 25-35 minutes. Cool in pans on rack for 10 minutes. Turn out and finish cooling on racks. Nestle Crunch Bar Frosting: Melt broken up candy bars in top of double boiler; stir in sour cream. Remove from heat; add vanilla and beat until cool and creamy. Frost thickly between layers, on sides and top of cooled cake.