Surprise Cake

Preheat the oven to 160°C fan (or 180°C conventional) and prepare a wire rack.

Separate the eggs and put the egg whites into a clean, fat-free mixing bowl.

Beat the yolks until foamy and gradually add the sugar until the mixture is pale and creamy.

Add the vanilla sugar, oil and milk to the yolk mixture and mix briefly.

Mix the flour and baking powder, add to the mixture and stir only until a smooth batter forms.

Whip the egg whites until stiff and gently fold them into the batter until no large streaks remain.

Divide the batter into three equal portions and color one third intensely with blue food coloring.

Alternate spooning the batter into the springform: start with two tablespoons of the light batter, then place one tablespoon of blue batter exactly in the center, and continue until all batter is used.

Bake the cake on the middle rack for 50–60 minutes.

Remove the cake from the oven, let it cool briefly in the pan, then release it from the springform and cool completely on a wire rack.

Decorate the cooled cake as desired and serve.