Heat the milk in a saucepan with the vanilla seeds, these are made when you opened and scraped the pod.
In a bowl put 5 yolks and sugar and mix thoroughly.
Add the cornstarch and stir to incorporate it.
As soon as the milk is hot enough, pour it flush into the bowl with the eggs and stir constantly to avoid creating lumps.
Put everything back in the saucepan and cook over medium heat, stirring constantly until your cream has thickened.
Turn off the stove, transfer the cream to a large plate and cover it with plastic wrap in direct contact with the cream, so that it does not dry out.
Let it cool completely.
Place a sheet of pastry in a square cake pan (8 inches) lined with parchment paper ( I used a squared pan but you can also use a round one)
Prick the bottom of the pastry with the prongs of a fork, and pour the cream, leveling it.
Place the black cherries accordingly.
Cover with the other sheet of puff pastry, making it adhere to the underlying sheet.
Beat the leftover yolk in a small bowl and brush it on the surface of the cake.
Bake in a hot oven at 180°C (356°F) for 35 minutes until the pasta is cooked and golden brown
Remove from the oven, let cool and transfer your puff pastry with cream and black cherries on a serving plate.
Decorate with icing sugar to taste and serve.