Profiteroles

Set the oven to 200 °C.
Place the butter and water in a heavy-based saucepan. Heat over a medium to low heat. The butter should melt before the mixture starts to boil. As soon as the liquid starts to boil, remove from the heat and add the flour all at once. Stir well with a wooden spoon.
Return the saucepan to the heat and stir over a low heat for two minutes. The mixture should leave the sides and bottom of the pan to form a ball. Set aside to cool. Add the beaten egg, a little at a time, beating with a wooden spoon. The mixture should be smooth and shiny.
To make the filling, bring the milk to the boil in a sacepan. While the milk is heating, beat together the egg yolks and castor sugar until light. Beat in the flour. Beat in the hot milk, a little at a time. Return the mixture to the saucepan and cook over a medium to low heat, whisking continuously. Once the mixture is thick and comes to the boil, remove from the heat and beat in the vanilla essence. Remove from the heat and cool. Whip the cream until soft peaks form, then fold it into the custard.
Put teaspoonfuls of the mixture onto a greased baking tray. Place the tray in a preheated oven and reduce the heat to 170 °C. Bake for 15 to 20 minutes until crisp and golden. Remove from the oven and cut a slit into each one to allow steam to escape. Cool until read to fill. Fill each pastry with a dollop of custard.
Spoon the cream into the pastries and stand on a wire rack. Melt the chocolate in a glass bowl over a saucepan of simmering water or in the microwave oven. Stir until smooth and allow to cool slightly. Drizzle spoonfuls of chocolate over the pastries. Allow to set before serving. Store the filled pastries in the fridge until ready to serve.