Doberge cake

1/2 c. butter
  1/2 c. shortening
  2 c. sugar
  1/4 tsp. salt
  4 eggs, separated
  3 c. sifted cake flour
  3 tsp. baking powder
  1/2 c. milk
  1/2 c. water
  1 tsp. vanilla
  FILLING:
  4 squares unsweetened chocolate
  1 qt. milk
  1/2 c. flour
  1 1/2 c. sugar
  2 eggs, beaten
  CHOCOLATE FROSTING FOR DOBERGE:
  1/4 c. butter
  4 squares unsweetened chocolate
  1 lb. confectioners' sugar
  1/2 c. boiling water
     Beat egg whites until stiff and set aside.  Cream butter,
  shortening and sugar with electric mixer.  Add eggs yolks, one at a
  time.  Add milk and water alternately with flour until completely
  mixed.  Fold in beaten egg whites and vanilla.  Bake in 4 (8") pans
  at 350 degrees for 25 minutes.  Cool.  The layers must be split.
  This is easier to do if they are placed in the freezer for a short
  time before cutting them.  Split each layer and spread with the
  following filling.  As the layers are stacked with the filling, put
  cut layer against baked layer so the cake will stay put.  Melt
  chocolate.  Combine flour and sugar in a separate saucepan.  Add
  milk to the flour mixture and cook until thickened.  Add a little of
  this mixture to the beaten eggs so they will not cook, then put the
  egg mixture back in the pan and cook until very thick.  Add the
  melted chocolate and stir well.  Cool before spreading on cake
  layers.  Melt butter and chocolate on low temperature.  Blend in
  sugar and water and heat until smooth.  Frost the top and sides of
  the cake.