Preparation: 15 minutes
Cooking time: 20 minutes
Refrigeration. Recommended
 

1. Preheat the oven to 210° C (425° F). Place a bowl in the freezer.
2. Unroll the puff pastry onto a floured surface. Form into a rectangle, then cut the rectangle into 3 equal pieces.
3. Prick with a fork to prevent it from puffing up too much, then place on a moistened baking sheet covered with parchment paper or a silicone mat.
4. Bake for about 20 minutes until lightly browned. Cool on a baking rack.

Pastry cream

1. While the pastry is baking, make the pastry cream. Heat the milk over medium heat and add the vanilla sugar.
2. Whisk the egg yolks and sugar together. Whisk in the flour and cornstarch.
3. Slowly whisk in the hot milk.
4. Pour the mixture back into the saucepan and cook over medium heat, stirring constantly, until thickened.
5. Once the pastry cream is cooked, pour it into a clean container and refrigerate, covered with plastic wrap.
6. Pour the chilled cream into the cold bowl and whip until stiff and doubled in volume.
7. Whisk in the vanilla sugar. Fold gently into the pastry cream to form a light mousse.

Assembly

1.  Using a spatula, spread half the filling over one of the pastry rectangles.
2. Cover with a second rectangle and spread the remaining pastry cream on top. Top with the remaining rectangle.
3. Sprinkle the top with icing sugar. Refrigerate. Remove from the refrigerator 10 minutes before serving.