step 1
Put all the biscuits into a strong plastic bag and crush with a rolling pin until they look like fine breadcrumbs. Tip into a mixing bowl.
step 2
Melt the butter in a small saucepan and pour over the biscuit crumbs. Mix well and press into a 20cm loose-bottomed tin. Leave in the fridge to set for at least an hour.
step 3
Put the mascarpone and condensed milk into a large bowl. Carefully grate the lemon and limes and and add the zest, then squeeze in the juice as well.
step 4
Beat everything together until it is smooth and thick, then spread it over the biscuit base and chill in the fridge for at least another hour.
step 5
Decorate the top with fresh fruit or make chocolate shavings by scraping a bar of chocolate with a vegetable peeler.