Masterclass key lime pie

Pre-heat the oven to 160C/140C Fan/Gas 3. Lightly grease a 23cm loose-based flan tin with butter. Put the biscuits in a freezer bag and bash with a rolling pin to make crumbs. Melt the butter and stir in the crumbs and sugar. Transfer to the tin and use the back of a metal spoon to press the mixture firmly over the base and up the sides to an even thickness. Put on a baking tray and cook in the oven for 10 minutes. Allow to cool.

Separate the eggs and put the yolks in a large bowl. Add the condensed milk, making sure you get all of it out of the can. Always use original full-fat sweetened condensed milk for this recipe and not the 'light' version. Add the lime zest and whisk gently for about 2 minutes, using a hand or electric whisk, until everything is evenly combined.

Add the lime juice gradually, drizzling it in slowly and whisking gently all the time. While you're whisking, the mixture will start to thicken as the lime juice reacts with the condensed milk. The mixture will be quite pale. If you want to give your pie filling a little more colour, add a few drops of green food colouring, although you can leave it out if you prefer.

Pour into the flan case, making sure you get all the mixture out with a spatula. Bake for 20 minutes or until the filling is just set. Leave to cool, then refrigerate. Before serving, whip the cream until it just holds its shape, taking care not to overwhip or let it get too stiff. Put the cream in a piping bag with a plain nozzle (or in a freezer bag with one corner cut off) and pipe small blobs around the edge of the pie.