1. Heat oven to 200 degrees. Place Swiss Meringue in an 18-inch pastry bag fitted with a large round tip (Wilton #1A). Line two baking sheets with parchment. Pipe meringue, forming domes 1 to 2 inches in diameter. Pipe a stem shape for each dome. Place baking sheets in oven for 1 hour, reduce heat to 175 degrees, and continue baking until meringues are completely dry to the touch but not browned, 45 to 60 minutes.

2. Fill a medium saucepan one quarter full with water. Set over medium heat, and bring water to a simmer. Place bittersweet chocolate in a heat-proof bowl, and set over simmering water. Turn off heat; stir occasionally until completely melted. Using an offset spatula, spread bottoms of domed meringues with chocolate; let set at room temperature.

3. Place white chocolate in a heat-proof bowl, and set over simmering water. Turn off heat; stir occasionally until completely melted. Allow to cool slightly. Spread white chocolate over dark chocolate; use a toothpick to create lines from the center of the cap to the edges. Let set in a cool, dry place.

4. Poke a small hole in the center of each mushroom cap using a paring knife. Dip the pointed end of each of the mushroom stems in melted white chocolate, and insert into hole in center of cap. Allow to set. Meringue mushrooms should be kept in an airtight container in a cool, dry place.