In the bowl of a stand mixer, add the eggs and sugar. Whisk 10 minutes until the mixture whitens and doubles in volume, then turn the power off.
Gently incorporate the flour and the cornstarch with a spatula so as not to break the foamy appearance.
Pour the mixture into 3 molds and bake for 20 minutes. Check the cake with the tip of a knife. It should come out clean.
Wait a few minutes and unmold on a cooling rack.
When the cake bases have completely cooled, cover tightly with plastic wrap and set aside for assembly.
Place all the ingredients (water, sugar and lemon juice) in a saucepan and bring the mixture to a boil for about 3 minutes.
Cool and then generously brush the cake bases.
Pastry cream (the day before)
In a saucepan, bring the milk to a boil with the split and scraped vanilla pod.
In a bowl, off the heat, whisk together the sugar and flour. Add the egg and egg yolks and whisk until the mixture is smooth and homogeneous.
Gradually add the hot milk while whisking.
Transfer the mixture to the saucepan and whisk constantly over medium heat, being careful to scrape the bottom and edges of the pan. Simmer for 1 to 2 minutes over low heat until the cream has thickened.
Off the heat, add the butter to the preparation until you obtain a homogeneous preparation.
Pour the pastry cream into a large bowl.Cover with plastic wrap, pressing it directly onto the surface of the pastry cream to prevent a skin from forming. Let cool.
Refrigerate until cool, about 3 to 4 hours.
Fill a pastry bag with the pastry cream. Set aside.
Mascarpone whipped cream (the same day)
In a bowl (or the bowl of a stand mixer), add the mascarpone, the cold cream and the vanilla.
Start whipping, first at low speed, then increase the speed of the mixer to medium speed. Midway, add the icing sugar.
Place a layer of Genoise cake on a plate. Thoroughly brush the biscuit with syrup.
Apply the pastry cream evenly over the cake surface with the help of the pastry bag and smooth out with a spatula.
Wash, trim and quarter the strawberries. Spread the strawberries evenly over the pastry cream.
Cover the strawberries with 2 to 3 tablespoons of light whipped cream and smooth out with the spatula.
Place a layer of Genoise cake on top. Proceed the same way on the second layer.
For the final Genoise layer, cover the sides of the cake with whipped cream. Fill a pastry bag with an open star tip, with mascarpone whipped cream.
Apply the mascarpone whipped cream wth the design of your choice. Spread the remaining strawberries on top of the cake, starting from the outside and going inside.
In some parts of Sweden, raspberries, bananas and passion fruit are added to the cake.