Preheat the oven to 230°C. Separate the egg whites from the yolks. Beat the yolks with 2 tbsp of granulated sugar until a white and frothy mixture forms. Whip the egg whites until foamy. Start at low speed and increase the speed as you add 150 g of granulated sugar. Continue whipping until you no longer feel any sugar granules between your fingers. Add the egg yolks and the sifted flour. Mix gently.
Place the dough in a piping bag. Pipe the dough into rolls about 5 mm apart, lengthwise, onto the baking sheet lined with parchment paper. Dust generously with powdered sugar. Bake in the oven for 5 minutes. Turn the biscuit onto a damp and wrung-out kitchen towel. Do not remove the parchment paper and let it cool on a flat surface.
Whip the cream stiff with the instant coffee and 2 tbsp of granulated sugar. Place the biscuit on a new sheet of parchment paper, with the ribbed side facing down. Spread with the cream. Crush the glazed chestnuts (set some aside for decoration) and distribute them over the cream. Carefully but tightly roll up using the parchment paper. Let it rest well covered in the refrigerator for at least 3 hours.
Cut the ends of the Christmas log, place it on a serving platter. Whip 100 g of egg whites to foam with 100 g of granulated sugar and then add the powdered sugar. Whip for a few minutes until a shiny and firm mass forms. Pipe or spoon dollops onto the Christmas log. Brown with a burner and finish with the glazed chestnuts.