Whisper Cake with Chestnut

Preheat the oven to a low temperature (130°F)

For two large baking sheets, line with parchment paper and make the meringue mixture: Beat egg whites in a bowl until stiff peaks form

Add 1 tablespoon of sugar and beat for another minute, or until the mixture becomes shiny

Gradually add the remaining sugar with a spoon

Divide the mixture into two equal parts and, using a piping bag, make two spiral circles, each 9 inches in diameter, on the parchment paper on the baking sheets

Bake the meringue for 50-60 minutes, or until it is dry and lightly golden

Let cool and remove from parchment paper

Cut the chestnuts into slices, cover with cold water, bring to a boil, then simmer until tender

Remove from heat, peel, and strain through a sieve (if using sweet potatoes, cook as usual, peel, and reserve)

In a small saucepan, combine sugar and water, bring to a boil, and let simmer

Allow to cool, then add to the chestnut or sweet potato puree, along with vanilla extract (if using sweet potatoes, add chocolate powder at this point)

If desired, blend the chestnuts (or sweet potatoes) in a blender with the sugar syrup

Mix half of the whipped cream into the puree and place between the two meringue circles, forming a sandwich

Dust the top with confectioner's sugar and chocolate shavings

Use a piping bag to decorate around the cake with the remaining whipped cream, forming 6 peaks.