Vanilla Custard Slice: Rachel Allen

Method

1. First, make the crème pâtissière. Pour the milk into a saucepan and add the split vanilla pod, if using. If using the vanilla extract, add it in with the butter at the end. Bring the milk mixture to the boil, then remove from the heat.
2. Whisk the sugar, egg yolks and cornflour together in a large bowl for about 2–3 minutes using a hand-held electric beater or electric food mixer until pale and light.
3. Next, pour the hot milk onto the egg mixture, whisking continuously, then return the mixture to the saucepan. Cook the mixture over a low heat, stirring continuously, until the mixture becomes thick. It will just come to the boil. If it boils unevenly or too quickly, it may become lumpy, in which case use a whisk to mix until smooth again.
4. Remove the custard from the heat and pour into a bowl (push the mixture through a sieve if there are any lumps). Add the pinch of salt and the butter and stir until melted and thoroughly combined.
5. Leave to cool, cover with cling film and then chill before using.
6. Preheat the oven to 220°C (425°F), Gas mark 7. Line two baking trays with baking parchment.
7. Divide the pastry into two equal pieces and roll out both pieces to 20cm (8in) square and 3mm (1/8in) thick. If you're using a sheet of ready-rolled pastry, then chances are it may be a rectangle measuring 18 x 46cm (7 x 18in). In which case, cut it in half so that you have two 23 x 18cm (9 x 7in) pieces, then roll each piece so that they are about 20cm square. Place each pastry sheet onto the lined baking trays, prick each piece a few times with a fork and chill for 10–15 minutes.
8. Bake the pastry sheets for 10–15 minutes or until golden brown and crisp. Set aside to cool.
9. While the pastry bakes, line the deep square tin with foil, allowing plenty of extra foil at the sides (the extra foil allows you to lift out the assembled slices). If you don't have a square tin, it's not the end of the world, just use the foil to make a base and sides.
10. Place one pastry sheet in the bottom of the lined tin (reserve the prettiest piece for the top). Spread the crème pâtissière evenly onto the pastry in the baking tray before placing the other piece of pastry on top. Refrigerate while making the icing.
11. For the icing, sift the icing sugar into a bowl. Stir in 3–4 teaspoons cold water – just enough to give you a thick, drizzling consistency – and set aside.
12. Place the chocolate in a bowl sitting over a saucepan with a few centimetres of water. Bring the water up to the boil, then take off the heat and allow the chocolate to melt slowly. Transfer the melted chocolate into a piping bag fitted with a very small plain nozzle and set aside to firm up slightly.
13. Take the custard slice from the fridge and spread the icing over the top layer of pastry. A palette knife or spatula dipped into boiling water is handy for helping the icing to spread.
14. Using the piping bag, draw ten parallel lines with the melted chocolate along the top of the icing in one direction. Using the top of a toothpick, 'drag' the lines of chocolate across the icing in alternating directions in about 2cm (3/4in) intervals to create a feathered effect. Place the slice back into the fridge to set.
15. Cut the finished custard slice into eight pieces. Using the foil, carefully lift the portioned vanilla slices out of the tray and serve.