Melt the butter in a saucepan and take the pan off the heat.
Blitz the biscuits to fine crumbs, and stir them together with the butter and the finely grated lemon zest. Divide the crumbs between 6 serving glasses.
Limoncello cheesecake
Put the cream cheese, cream, icing sugar, vanilla sugar, lemon juice and limoncello in a bowl, and whisk together until the cream thickens. Take care not to over-whisk.Taste the cream to see whether you would like a little more limoncello - some are stronger than others.
Spoon the cheesecake cream into a piping bag (it is the easiest way to control it), and pipe the cream on top of the biscuit crumbs.
Use a teaspoon to make a hollow in the top of each cheesecake, and fill it with lemon curd.
Sprinkle with white chocolate, and decorate with mint and a little edible glitter if you like.