If using frozen, defrost all but 2 tablespoons of the blueberries.
Preheat oven to 200 degrees C. Line a baking tray with baking parchment.
Beat egg yolks with 125g of sugar and vanilla until fluffy. Beat the egg whites until stiff with 40g sugar. Gently mix the egg whites in the egg yolk-sugar mixture.
Sift the flour and cornflour into a bowl and then fold them into the batter. Spread batter evenly over the prepared pan. Lightly bake in preheated oven for about 12 minutes. Put the cooked cake immediately after baking onto a damp tea towel and remove the baking parchment carefully.
Whip 200ml cream. Mix the yoghurt with sugar.
Soak the gelatine for about 3 minutes in cold water and let swell. Dissolve the gelatine in a small pot over low heat with just enough water to mix it.
Put the gelatine in a bowl and mix with just a few spoons of yoghurt mixture, then stir in the remaining yoghurt. Fold in blueberries. Fold in the whipping cream.
Leave the mixture in the refrigerator for a few minutes and only once the yoghurt mixture begins to gel spread on the pastry. Gently roll the sponge from the longer side.
Beat the rest of the cream with the vanilla sugar and spread it around the roll. Decorate with grated chocolate, cream and remaining blueberries. Leave for at least two hours in the refrigerator until set.