- With the rack in the middle position, preheat the oven to 250°F (120°C). Line a baking sheet with parchment paper. On the underside of the parchment paper, draw an 8-inch (20 cm) circle using a pencil.
- In a small bowl, combine the cornstarch and vinegar. Set aside.
- In another bowl, beat the egg white with an electric mixer until soft peaks form. Gradually add the sugar, beating until stiff peaks form. With a spatula, gently fold in the cornstarch mixture.
- With the spatula, shape the meringue into a disc inside the circle, inch (1 cm) from the line.
- Bake for 2 hours. Turn off the oven and let the meringue dry for 1 hour, leaving the oven door slightly ajar using a wooden spoon, or until the meringue is crisp and easily peels off the parchment paper. Let cool completely on a wire rack.
- Line a bowl with a 9-inch (23 cm) wide opening with plastic wrap.
- In another bowl, whip the cream, sugar and vanilla seeds with an electric mixer until stiff peaks form.
- Spoon the whipped cream into the lined bowl. Place the meringue disc onto the cream, flat side up, and press lightly. Freeze for 4 hours.
- In a food processor, purée all the ingredients until very smooth. Spoon into a pastry bag fitted with a 2- to 3-mm plain round tip. Set aside.
- Remove the bowl from the freezer and let it sit on the counter for 5 minutes. Unmould the whipped cream and meringue base.
- Place on a serving platter, meringue side down. Remove the plastic wrap. Pipe the chestnut topping in overlapping circles over the entire surface of the cake until completely covered. Refrigerate for 30 minutes or freeze. If frozen, leave the cake at room temperature for 30 minutes.
- When ready to serve, dust with icing sugar.