Grease a 15- x 10- x 1-inch jellyroll pan; line with waxed paper and grease lightly.
Combine first 3 ingredients; beat at medium speed of electric mixer. Gradually add 3 / 4 cup sugar, beating until thick and light colored. Fold in flour, cocoa, and vanilla.
Spread mixture evenly into prepared pan. Bake at 400° for 13 minutes or until surface springs back when gently pressed.
Sift 2 to 3 tablespoons powdered sugar in a 15- x 10-inch rectangle on a linen towel. Turn cake out onto sugar; remove waxed paper from cake. Trim crisp edges, if necessary. Starting with the short end, carefully roll cake and towel, jellyroll fashion. Cool thoroughly on wire rack. Unroll and remove towel; spread with whipped cream, and re-roll. Chill.
Dissolve coffee granules in boiling water; stir well, and set aside.
Melt chocolate in top of a double boiler; add butter, coffee mixture, and salt, stirring until smooth. Cool to lukewarm. Stir in about 2 1/2 cups sifted powdered sugar to make a spreading consistency.
Spread frosting evenly over cake. Mark with spatula or tines of a fork to resemble bark of a tree. Garnish with candied cherries. Refrigerate until serving time.
Note: In photograph shown, we used bay leaves, pomegranate seeds, and grated chocolate as rustic garnishes.