Rhubarb and custard profiterole tower

Preheat oven to 200°C (180°C fan) mark 6. Line two large baking sheets with baking  parchment. Sift flour into a large bowl. 

Put a pan over high heat. Pour in 225ml (8fl oz) boiling water from the kettle and add butter. Cover and bring to boil. As soon as it’s boiling, take off heat, quickly add flour and beat vigorously with a wooden spoon until glossy and smooth. Spoon back into empty flour bowl and set aside to cool for 15min. 

Gradually beat eggs into cooled flour mixture until smooth and glossy. Spoon into a piping bag fitted with a 1cm (½in) plain nozzle. Pipe 24 mounds on to prepared sheets, each  about 3cm (1¼in) wide and 3cm (1¼in) tall, spacing apart. With a damp finger, flatten   peaks. Bake for 20-25min until puffed and golden. 

Remove from oven and, when cool enough to handle, pierce a central 5mm (¼in) hole in bases with a skewer to allow steam to escape. Return buns to oven, holes up, for 3min. Cool completely on wire rack. 

Meanwhile, in a medium pan, mix rhubarb and sugar. Set aside for 5min. Gently heat, stirring, for 5min, then simmer for 10min until rhubarb is broken down and juicy. Spoon 3tbsp of rhubarb juice into a cup with cornflour and mix. Return cornflour mixture to pan and boil for 1min, stirring, until thickened. Pour into a large bowl, add custard and fold in to marble. Leave to cool. 

Spoon filling into a piping bag fitted with a 5mm (¼in) star nozzle. Pipe filling into skewered holes, filling buns, then arrange on a serving plate. Drizzle over chocolate, then scatter over sweets, if using. Serve.