*** Cake *** Cream the butter and sugar until fluffy. Add the yolks and vanilla, beat well. Heat chocolate and water, stir until smooth. Add to the cream mixture. Sift dry ingredients and to the cream mixture alternately with the milk, beginning and ending with dry ingredients. Beat whites until stiff, fold in batter. Place in a greased and floured 10-inch round pan. Bake in a preheated 350oF oven for 30-35 minutes, until test done. When cake is cooled, cut carefully into 3 layers. *** Filling *** Combine flour, sugar and salt. Gradually stir in the milk and cook over medium heat stirring constantly until thickened. Cook 2 more minutes. Stir a little of the hot mixture into the egg yolks and return to pan and cook 1 minute more. DO NOT BOIL. Add vanilla and cool completely. Spread between the layers. *** Chocolate Butter Cream Frosting *** Cream the butter and add 1/3 of the sugar, beat well. Add all remaining ingredients except the sugar, beat until smooth. Gradually add remaining sugar and beat until smooth. Spread on tope and sides of the cake. Refrigerate until ready to serve.