In a large bowl, whip cream, 1/2 cup confectioners' sugar, and 1 teaspoon vanilla until thick and stiff. Refrigerate.
Heat cream in a saucepan and pour over the chocolate chips. Stir until evenly melted and let cool to spreading consistency.
Unroll the cake, and spread the filling to within 1 inch of the edge. Roll the cake up with the filling inside. Place seam side down onto a serving plate, Place cake on serving platter; cut off both ends, one straight across and one at a diagonal. Position diagonally cut piece against side of cake roll and straight cut piece on top using about 1 tablespoon ganache to attach to cake. Frost cake with remaining ganache. With tines of fork, make strokes in ganache to look like tree bark. Sprinkle with powdered sugar and decorate with rosemary, meringue mushrooms, pinecones, or cranberries.