Rhubarb and custard slices

Method

1. Heat the oven to 200°C/180°Cfan/gas 6. Cut the pastry sheet into 2 even squares (roll it out slightly if needed) then set on the prepared trays. Cover each sheet with a piece of baking paper and put another baking tray on each to weigh down the pastry and keep it flat while baking (work in batches if you don’t have enough trays).
2. Bake for 25 minutes or until the pastry is golden and cooked through, swapping trays halfway. Remove the tray weights and the top sheets of paper, then take the pastry out of the tray, peel off the bottom paper and set aside to cool completely on a wire rack.
3. Soak the gelatine in a small bowl of water for 5 minutes to soften.
4. To make the custard, whisk the cornflour, sugar, egg yolks and vanilla to a thick paste in a large heatproof bowl. Put the milk and cream in a saucepan over a medium heat and bring to just below boiling. Gradually whisk the warm milk into the cornflour mixture until smooth.
5. Return the milk mixture to the saucepan, then set on a medium heat and bring to the boil, whisking constantly until thickened (about 5 minutes). Squeeze the excess water from the gelatine, then stir into the pan with the butter. Whisk until melted and combined, then remove from the heat.
6. Using a serrated knife, trim the pastry to fit the prepared tin. Put 1 piece in the base of the prepared tin, then pour over the custard and set aside for 15 minutes to cool slightly. Set the remaining piece of pastry on top, cover and chill until firm (about 4 hours or overnight).
7. To make the rhubarb compote, put all the ingredients in a pan, then stir and bring to a simmer. Cover, remove from the heat and set aside, still covered, for at least 10 minutes or until cool (see Make Ahead).
8. To make the icing, whisk 200g of the icing sugar with 40ml of the juice or water until smooth. In a separate bowl, whisk the remaining icing sugar with the remaining juice or water and a little food colouring until smooth.
9. Pour the white icing over the cool pastry and spread using a palette knife or the back of a spoon to cover evenly. Scrape the coloured icing into the piping bag and pipe lines across the top, 1cm apart. Take your cocktail stick and drag it across the lines of icing to create the classic decoration (it’s known as feather icing). Leave to set (about 30 minutes).
10. Using a serrated knife, cut the custard pastry into slices, then serve each custard slice with a spoonful of compote.