Dissolve the coffee in the water. Beat the egg yolks until light and fluffy, then gradually add the sugar, beating until thick. Sift the dry ingredients together and add to the creamed mixture alternately with the coffee mixture, beating well after each addition. Add the vanilla and ground walnurs and then fold in the stiffly beaten egg whites until no white remains. Bake in 3 paper lined 9 X 4 cm rond pans in a slow oven (325 degrees F.) about 30 minutes or until done. Cool until cold. Fill the cooled cake with the Orange Filling; frost with the Mocha Frosting. Garnish with whole walnut halves ORANGE FILLING: Cream the butter until light and fluffy the ngradually add the confectioners' sugar, creaming well. Beat in the cocoa, instant coffee, cold water and orange juice, blending well. MOCHA FROSTING: Mix the confectioners' sugar, cocoa, and instant coffee, blending well. Add the water, melted butter, and vanilla. Beat until it reaches a spreading consistency.