Cream butter & margarine; gradually add sugar, beating well. Add eggs, one at a time, beating well after each addition. Combine flour, soda, cinnamon & nutmeg. Add flour mixture to creamed mixture alternately with buttermilk, beginning & ending with flour mixture. Stir in raisins & currants. Pour batter into 2 greased & floured 1 pound coffee cans, reserving 3 tbsp batter. Bake at 300 degrees for 1 hr & 10 min. Or until a toothpick inserted in the center comes out clean. Cool in cans 10 minutes; remove from cans & cool completely on a wire rack. Place 1 tbsp of reserved batter into each of 3 greased & floured miniature muffin pans. Bake at 300 degrees for 20 min. Cool in pans 10 min.; remove from pan & cool completely on a rack. Spread frosting on 1 end of each large cake. Place frosted ends together, forming one log. Spread remaining frosting, reserving 1/2 cup, over cake. Place miniature cakes on cake logs at intervals to represent knots; spread with reserved frosting. Score frosting with fork tines to resemble bark. Garnish with chocolate leaves, if desired. Yield: one 8 inch log cake To prepare frosting: Melt butter or margarine & chocolate in top of a double boiler. Add sugar, milk & salt; beat until smooth. Stir in vanilla. Yield: 1 1/2 cups