together with butter cream icing and dust lightly with cocoa in a fine strainer. Beat egg yolks and butter together until smooth. Add coffee and milk. Gradually add powdered sugar. Beat until smooth. Mix about 1/3 cup to 1/2 cup of the frosting with green food coloring for the ivy decoration. TO ASSEMBLE: Unroll cooled sponge, remove towel, spread, cake with butter cream icing. Roll up. Cut off at a diagonal, a 2" slice. This is the tree stump. Frost the outside, then add the stump and frost. Make ivy patterns. Add the mushrooms. Dust the whole cake very lightly with powdered sugar, to simulate snow. Keep in refrigerator. Cut with serrated knife.