This makes a stunning holiday centerpiece.
Have ready:
Combine:
Place the sheet cake right side up on a large sheet of parchment paper. Brush generously with the syrup. Spread with the 2 cups filling. Roll and wrap as for Cake Sheet for Roll Cakes. For easiest handling, freeze for at least 3 hours until semifrozen. It will keep, frozen, for up to 3 months.
When ready to decorate, let the frosting come to room temperature and stir or beat until smooth. Spread most of it over the cake roll, then texture it with a fork to look like tree bark. Use a sharp knife dipped in hot water to cut a 2-inch slice from each end of the roll. Set the cake roll on a serving plate. Place the reserved slices on either side of the cake roll to resemble stumps, using any remaining frosting to cover the joints. If serving immediately, decorate the log with:
Or refrigerate for up to 48 hours, remove from the refrigerator 2 to 3 hours before serving, and then decorate with the mushrooms.