Method

• 1.
  For the custard, whisk the egg yolks and caster sugar for 2-3 minutes until thick and pale, then whisk in the cornflour mixture. Heat milk in a pan with the vanilla pod and seeds. Bring to the boil, then remove from heat. Whisking vigorously, pour milk in a slow stream into the egg yolk mixture.
• 2.
  Return custard mixture to a clean pan over medium heat, whisking constantly until mixture starts to thicken. (Make sure you scrape the sides and bottom, otherwise the mixture will burn.) Once it releases a bubble or two, remove the pan from the heat. Discard vanilla pod, pour the custard into a bowl and set aside to cool. Spoon into a large piping bag fitted with a 1cm nozzle and chill for 1-2 hours
• 3.
  Preheat the oven to 200ºC. Line a baking tray with baking paper.
• 4.
  Roll out the pastry to a 24cm x 30cm rectangle, then cut into eighteen 10cm x 4cm rectangles and place on the tray, lightly brush with beaten egg, then sprinkle with 2 tbs caster sugar. Cover glazed rectangles with baking paper, then place another baking tray on top; this will stop the pastry rising. Bake for 30 minutes or until golden and crisp. (If your pastry doesn’t look quite done after 30 minutes, remove the baking paper and tray, and bake for a further 6-8 minutes.)
• 5.
  Meanwhile, toss rhubarb with remaining 1/4 cup (55g) caster sugar and place in a small baking dish. Roast on a shelf under pastry for 20 minutes or until tender but holds its shape. Cool completely.
• 6.
  To assemble, place a pastry rectangle onto serving plates, then place 3 rhubarb pieces over the pastry. Top with another pastry rectangle, then pipe over custard. Top with a third pastry rectangle. Repeat to make 6 mille-feuilles. Dust with icing sugar and serve immediately.