Step 1
First knead the biscuit dough. Place the butter, 400g flour and sugar in a large mixing bowl, then rub the flour and sugar into the butter using your hands. Continue until the texture resembles wet sand.
Step 2
3 Add lemon zest and mix. Add a small splash of cold water and continue mixing. You want the dough to come together – just add a little more water if you need to. Pat the dough into a disc, wrap in clingfilm and chill in the fridge for 30 minutes.
Step 3
Preheat the oven to 220°C/fan oven 200°C/mark 7. Dust your work surface and rolling pin with flour. Line 2 baking sheets with greaseproof paper.
Step 4
Roll out the biscuit dough so that it is about 4mm thick. Cut it into 2 rectangles that are slightly smaller than the baking sheet. Place a rectangle of biscuit dough on each sheet. Bake in the oven for about 12 minutes or until they are light golden.
Step 5
Measure the baking tin you will use to assemble the sandwich (I use a rectangular one that measures 33 x 23 cm). When the biscuits come out of the oven, cut them into the shape of your tin while the dough is still warm. Let them cool completely on the baking sheet.
Step 6
Meanwhile, make the ice cream. Pour the cream into a large saucepan with the sugar and a pinch of salt. Bring to a simmer, stirring to dissolve the sugar. When the sugar has dissolved, remove the pan from the heat and add the lemon juice and the zest of 1 lemon. It will thicken immediately. Pour into a freezer-proof container and allow to cool completely. Then chill in the fridge until you come to assemble the ice cream.
Step 7
When the biscuit and ice cream mixture has cooled, line a baking tin with clingfilm. Place a biscuit sheet in the base of the tin, then spoon over the ice cream. Place another biscuit on top, then freeze flat for at least 8 hours and preferably overnight.
Step 8
When you come to serve, remove the tin from the freezer and leave for 10 minutes. Shimmy the ice cream and biscuit block out of the tin. Using a sharp knife, slice the sandwich into halves (you’ll want to run it under hot water.
