roasted rhubarb or other seasonal fruit, for the topping
Whizz together the biscuits or crush in a sealed bag until you get fine crumbs. Gently melt the butter, then mix into the crumbs. Press evenly into a 20cm loosebottomed round cake tin. Chill in the fridge while you make the filling.
Put the remaining ingredients into a food processor and whizz until smooth. Spread over the base, then smooth the top with a knife. Leave in the fridge overnight to set. Remove the cake from the tin and top with roasted rhubarb (recipe, below) or your choice of fruit.