In a bowl: Whisk the egg yolks and sugar until pale. Add the cornstarch and mix. In a saucepan: Bring the milk and caramel to a boil. Pour half of the milk over the eggs, mix. Return everything to the saucepan.

Roll out the puff pastry in your baking dish, preferably a deep one. Prick the pastry with a fork and pour the mixture over the pastry. Bake for 45 minutes at 350°F (180°C).