Preheat the oven at 250 degrees Celsius.
Start to make the cake by whipping the sugar and the eggs fluffy and white.
Add the potato flour, flour, baking powder and the water and stir together.
Place a baking paper on a baking sheet. Pour evenly the batter on the paper and place in the middle of the oven for 5 minutes.
Take out the cake and sprinkle it with some sugar.
Place it upside down on a baking paper. Pull away the paper it was baked on. Let the cake cool down.
Time to make the filling by whipping the cream and the vanilla sugar to a firm foam.
Add the raspberries and mix gently together.
Place evenly on the cake and roll together from the long side. Wrap the rulltårta with plastic foil to keep together. Place cold in the fridge for minimum 1 hour.
Whip the rest of the whip cream and 1 teaspoon of vanilla sugar together, pour in a piping bag.
Take out the cake and place on a serving plate. Decorate the cake with the whip cream and raspberries.
Cut the rulltårta in slices and decorate the cake with some more whipped cream and raspberries on the plates before serving it.