To make sugar syrup, combine the sugar and water in a small saucepan and bring to a boil. Remove from the heat, add vanilla extract or another flavoring, and let it cool to room temperature, then refrigerate.

Place an 8-inch (20 cm) cake ring (springform pan or mousse cake mold) on a serving plate or a cake board. Cut about 20 ladyfinger biscuits at the base to be 2.8 inches (7 cm) high using a serrated knife. Place lady fingers around the edge of the cake ring, the sugared side towards the mold.

Pour the cold syrup into a deep plate. Dip biscuits, one at a time, on both sides, counting to 3 to ensure that they do not oversoak. Arrange dipped cookies in the bottom of the pan, sugared side up. Try to fill the gaps between cookies, cutting them into pieces.

To make chocolate mousse, chop dark chocolate with a knife or use a food processor. Place chocolate in a heat-proof large bowl and bring over a bain-marie or water bath. Melt chocolate, stirring occasionally with a wooden spoon, then let it cool on the counter. Alternatively, use a double boiler or a microwave to melt chocolate at 30 seconds intervals on 30% power.

Place whole eggs with egg yolks in a mixing bowl and beat with a hand whisk until frothy. At the same time, pour water with sugar in a small saucepan and bring over medium-high heat. Cook the sugar syrup until 250°F (121°C), checking the temperature with a cooking thermometer.

Pour the hot syrup over the eggs, whisking constantly, and beat until the mixture whitens, doubles in volume, and cools completely. Add the melted chocolate in 3 times and gently mix with a rubber spatula, lifting the mass until you obtain a nice homogeneous foam.

Place cold heavy cream in the bowl of a stand mixer fitted with a whisk attachment (you can use a hand mixer) and whip the cream until soft peaks (not stiff peaks). Pour the chocolate mixture into the whipped cream and gently mix with a spatula.

To assemble Charlotte, pour half of the chocolate mousse into the prepared mold. Add a layer of dipped cookies with a flat side up. Pour the remaining mousse and smooth it with a spatula or the back of a spoon. Refrigerate Charlotte for 4-6 hours, ideally overnight.

Make dark chocolate shavings out of the chocolate bar using a small sharp knife or a vegetable peeler. Remove the ring and sprinkle chocolate shavings on top of the mousse. Wrap the dessert with a ribbon for a pretty decorative touch.