Preheat the oven to 220°C (Gas Mark 7-8).
Divide the flaky pastry into six 12 cm diameter discs and pierce them using a fork.
Divide the butter into small pieces. In a pan, pour 200ml water, a pinch of sugar, a pinch of salt and 100g butter. Bring to the boil and remove from the heat. Add the flour and mix in with a wooden spoon. Return to the heat and mix until it no longer sticks to the bottom of the pan. Pour into a mixing bowl and add 4 eggs one by one, mixing briskly.
Using a pastry bag, lay 6 puff pastry circles on the flaky pastry discs.
Prepare 3 or 4 small buns per person with the remaining pastry mixture on another baking tray. Using a pastry brush, glaze them with egg yolk and bake for 15 to 20 minutes at 220°C.
Soak the gelatine in cold water. Infuse the vanilla into the milk and boil. Blanch 5 egg yolks with 100 g sugar and then add 40 g flour. Mix in the hot milk and return to the pan. Bring to the boil and cook for 3 minutes. Add the gelatine and 50 g butter, cover with cling film and leave to cool.
Whisk the cream, and add to the pastry cream mixture gradually once it has cooled. Pierce the pastry and the buns and fill them with the cream using a piping bag.
Heat 150g sugar in a pan (without stirring) until you obtain a golden caramel. Dip the buns into the caramel.
Lay the buns on the pastry crowns and serve.
«Take care when caramelising sugar; do not stir while heating.»