Betty’s Swiss Roll with Fluffy Raspberry-Blueberry Cream Filling

1. Preheat the oven to 220°C. Line the base of the tin (about 15 x 12in) with baking parchment. Put the frozen raspberries into a medium size bowl. Add vanilla sugar, one tablespoon of lemon juice and one tablespoon of lime juice to the frozen raspberries. Set aside.
2. Separate the egg whites from the egg yolks. Put the egg yolks into a large bowl and put the egg whites into a medium sized bowl.
3. Add sugar, one pinch of salt and warm water to the egg yolks. Whisk until light and fluffy. Add zest of 1/2 lemon and 1 lime. Set aside.
4. Add a pinch of salt to the egg whites and whisk with an electric whisk until stiff. Put the whipped egg whites on top of the egg yolk-mixture.
5. Sift the flour on top. Gently fold in and combine, trying to keep the volume.
6. Pour the mixture into the tin and level into all the corners, smoothing the top with a palette knife.
7. Bake for 8-10 minutes in the middle rack of the oven until golden brown on top.
8. In the meantime, put the cream into a medium sized bowl and whip it until stiff. Add the now defrosted raspberries and gently continue to whisk. Add the cane sugar and mix to combine. Put into the fridge until needed.
9. Generously sprinkle a kitchen towel with additional white sugar (take as much as you need to get the entire towel covered with a thin layer of sugar). Carefully turn the sponge out of its tin onto the towel. Immediately remove the baking parchment. Cover cake with the baking tin and let it cool down (for about 5 minutes).
10. Cut away the edges of the sponge to form a perfect rectangle. Spread the cream onto the sponge. Put fresh berries on top. Now gently, but firmly roll it up using both your hands. Cut away both ends if you want it to look extra-nice. Put the Swiss roll onto a platter and put it into the fridge until you want to serve it. Enjoy! (Or as we Swiss people would say “en guete”).