Preheat oven to 350°F. Grease a 9-inch springform pan with butter.
Separate the eggs. Beat the egg whites with a pinch of salt until stiff peaks form. In a separate bowl, whisk together the egg yolks, sugar, and vanilla sugar until light and frothy. Fold in the stiff egg whites.
Combine flour, cornstarch, and baking powder, then sift over the batter. Gently fold everything together and pour the batter into the springform pan.
Bake for about 20 minutes, then let cool completely.
Now, whisk together mascarpone, sugar, and vanilla sugar. Beat the heavy cream until stiff peaks form, then fold into the mascarpone cream. Grate the chocolate and stir into the mascarpone cream. Refrigerate until ready to use.
Remove the cake base from the pan and place it on a cake plate. Spread the mascarpone chocolate cream evenly over the base and smooth over with a spatula.
Wash and hull the strawberries. Slice them evenly. Arrange the slices in a fan shape on top of the cream, starting from the outside and working inwards.
Chill the cake for at least 1 hour. Decorate with fresh mint leaves before serving.
