Heat the oven to 180°C/Fan 160°C. Tip the biscuits, melted butter, caster and salt into a food processor and blitz to make fine crumbs, press into the tin firmly and bake for 10 minutes. Remove and allow to cool.
Increase the oven temperature to 220°C/Fan 180°C.
With an electric hand whisk or tabletop mixer beat the cream cheese on a low speed for about 2 minutes. Slowly add the caster sugar, when incorporated add the flour, making sure to scrape down the sides. Now add the vanilla extract, lemon zest, eggs, and the egg yolk, again scraping down to make sure all the ingredients are incorporated. Add the soured cream and whisk on low until just blended.
Pour in the filling and bake for ten minutes. Reduce the oven to 110°C/Fan 90°C and bake for a further 40 minutes. Leave to cool completely before decorating.
Make the Pimm's glaze. Put the Pimm’s, lemonade, grenadine and jam into a small saucepan and slowly bring to the boil. Boil for 8-10 minutes until reduced and syrupy. Strain into a jug and cool.
To decorate, Arrange the strawberries, raspberries, meringue pieces, coiled cucumber slices, and mint. Drizzle with the Pimm’s glaze to make your toppings glisten.