Cover a tray with baking paper and preheat the oven to 200°C hot air.

For the Swiss roll, beat the whole eggs in the mixer with the sugar and vanilla until fluffy, 5 minutes. At the same time, whisk in the sparkling water.

Mix flour with baking powder and salt. Gently stir/fold the flour mixture into the egg mixture. Don't stir too much.

Spread the biscuit mixture on the tray and spread evenly. Bake in the oven for 11-12 minutes until golden brown. 

Meanwhile, sprinkle a tea towel or a new sheet of baking paper with fine raw cane sugar. Immediately turn the baked sponge cake out of the oven onto the tea towel sprinkled with sugar.

Now take your little cleaner cloth and make it wet. Then gently spread the baking paper with the damp cloth until it is wet and soft. Now you can easily remove the parchment paper from the sponge cake. 

Spread the blueberry jam generously over the sponge cake and roll it up carefully. Leave to cool completely.

For the cream, whip the whipped cream until stiff. Mix the yogurt with the sugar, lemon zest, and lemon juice. Soak the gelatine in cold water for 3-4 minutes, squeeze it out, and heat it in 1-2 tablespoons of lemon juice in a saucepan until it has completely dissolved. Add 3 tablespoons of the yogurt to the gelatine in the saucepan and stir. Then add the gelatine mixture to the remaining yogurt mixture and stir. Finally, stir the whipped cream into the yogurt cream. Fold in 200 g of fresh blueberries. 

Line a round bowl (approx. 15 cm in diameter - with a nice dome shape) with cling film. 

Cut the Swiss roll into about 13-15 slices. Line the bowl all around with the Swiss roll slices (leaving 3-4 pieces). Fill in the yogurt cream. Top with the remaining Swiss roll slices.

Place the Charlotte in the bowl in the fridge for at least 5-6 hours (preferably overnight). 

Carefully invert the bowl onto a cake plate and remove the foil. If you like, decorate Charlotte with fresh heather berries and flowers.