Line a baking tray (30cm/11.8inch square baking tray) with baking paper. Prepare a piping bag with a round tip. Preheat an oven at 200°C/390°F. Sift the flour on the paper and set aside.
Separate eggs into the whites and yolks, make sure no egg yolk gets into the egg whites. Put the egg whites into a mixing bowl.
Add about one pinch of sugar into the egg white, then start whipping with the highest speed. Add the rest of sugar at two different times while you are making the meringue. Make the meringue at stiff peaks.
Once the meringue whipped properly, add the egg yolk, and just mix it a little.
Add the flour little by little and mix with the rubber spatula from bottom to top. Try to mix the batter as little as possible to prevent the cake from becoming dense. When you can’t see the flour anymore, you should stop mixing.
Transfer the batter into the piping bag, then pipe the batter with the same thickness line onto the baking tray. Pipe the batter onto all over the tray.
Sprinkle the powdered sugar generously over the batter. After one pass with sugar, much of the sugar will be absorbed, so go back over with one more sprinkling of powdered sugar.
Reduce the oven temperature to 190°C/375°F. Bake for about 10 to 12 minutes or until the surface looks to be dry and little crispy. You only need to cook until slightly golden. Transfer the sponge cake onto the rack immediately then place another baking paper onto the sponge cake. Let it cool at room temperature.
Put the whipping cream and caster sugar in a mixing bowl, whip until stiff peaks. Then mix in the plain yogurt. Keep the cream in the fridge until just before use.
Cut your favorite fruits into pieces.
Remove the baking paper from the bottom of the cake. Place browned side down, on a new piece of baking paper. Spread two-thirds of the cream onto the sponge. The rest of the cream is for decoration so keep it in the fridge. Place the fruits along the cream in a line to get the same beautiful surface.
Gently roll the sponge cake over the line of fruits. Press gently to make a beautiful roll shape. Make sure the edge of the sponge cake remains on the bottom.
Allow the cake to cool completely rolled up in the baking pepar. Place in the refrigerator at least 1 hour until cutting.
Decorate with the rest of cream and fruits.