1.To make custard cream, split vanilla bean lengthways, scrape seeds into milk in a small saucepan. Discard bean. Bring to the boil.
2.Beat egg yolks, sugar and cornflour in a small bowl with an electric mixer until thick. With motor operating, gradually beat in hot milk mixture. Return custard to pan; stir over heat until mixture boils and thickens. Cover surface with plastic wrap and refrigerate 1 hour.
3.Beat cream in a small bowl with an electric mixer until soft peaks form. Just before serving, fold cream into custard in two batches.
4.Preheat oven to 220°C. Grease two oven trays.
5.Combine half the butter and the water in a small saucepan. Bring to the boil. Add flour and beat with wooden spoon over heat until mixture comes away from side of pan and forms a smooth ball. Transfer mixture to a small bowl and beat in egg with an electric mixer until mixture becomes glossy.
6.Spoon pastry mixture into a piping bag fitted with a 1cm plain tube. Pipe 5cm lengths, about 5cm apart on trays. Bake 7 minutes.
7.Reduce oven to 180°C and bake a further 10 minutes. Using a serrated knife, cut éclairs in half, remove any soft centres and return to trays. Bake 5 minutes or until dry to touch. Cool on trays.
8.To make chocolate glaze, chocolates and remaining butter in a small heatproof bowl over a small saucepan of simmering water until smooth.
9.Spoon custard cream into a piping bag fitted with a 5mm fluted tube. Pipe custard cream into 16 pastry bases, top with pastry tops. Spread with chocolate glaze.
Assemble and serve éclairs as close to serving time as possible.Note