Lemon curd sandwich biscuits

Method

1. To make the curd, put the butter, sugar, zest and juice into a saucepan and set over a low heat. Stir a little to help the sugar dissolve. Before all the butter has melted, take 1 tbsp of the citrusy mixture and mix in a cup with the cornflour. Pour the beaten eggs and cornflour into the pan and gently whisk until the curd noticeably starts to thicken. (If making lime curd, you might want to add a little food colour now, for the ‘traffic light’ effect.)
2. As soon as the mixture thickens, pour into a bowl, cover and put in the fridge. Don’t worry if it looks a bit thin; it will thicken as it cools.
3. Then begin preparing the biscuits. Beat the butter and sugar in a bowl with an electric whisk until light-coloured and smooth. (If the butter is not at room temperature, chop it up, put into a jug of tepid water for 10 minutes to soften up, then drain off the water.) Add the egg, vanilla bean paste and lemon zest and continue to beat until fully incorporated (you will need to scrape down the sides of the bowl).
4. Sift the flour into the mixture and gently mix it in with a wooden spoon until fully combined, then shape into a ball by hand.
5. Roll out on to a floured sheet of baking parchment to around 5mm thick. Slide the parchment on to a baking sheet or tray and put it into the fridge for 10 minutes to firm up.
6. Remove from the fridge and press out your biscuit shapes using a 6cm cutter. You will need 12 bases and 12 tops with holes cut out of them using the 2cm cutters. Combine the offcuts and re-roll them on a floured work surface. Try to be fairly quick doing this, as the mixture will warm up and get sticky. (If it does, just pop it back in the fridge to firm up again.)
7. Arrange the shapes on 2 baking sheets or trays lined with baking parchment and cool in the fridge for another 20 minutes.
8. Preheat the oven to 190°C/fan 170°C/gas 5 and bake the biscuits for 7 minutes, then take both trays out. Sprinkle the ‘top’ biscuits (the ones with the holes) with caster sugar, then return both trays to the oven and cook for a further 5 minutes or until golden brown. Take out and transfer to a cooling rack with a palette knife. Allow to cool fully.
9. Assemble by spreading the lemon curd on the bottom biscuits and sandwiching the tops.Recipe from BIY: Bake it Yourself by Richard Burr (£10; Quadrille Publishing Limited)