Adapted from Leith’s Vegetarian Bible, p459
1. Crush the biscuits with a rolling pin or in a food processor. Melt the butter and mix with the biscuit crumbs. Spread over the base of a 17.5cm/7in or 20cm/8in spring-release cake tin, pressing down well.
2. Pare strips of lime zest from one of the limes and cut into fine shreds. Douse in boiling water, drain and pat dry on kitchen paper. Set aside. Grate the remaining zest from the limes and squeeze the juice.
3. Lightly whip the cream. Fold in half the condensed milk and the grated lime zest and juice. Sweeten to taste with extra condensed milk.
4. Pour the mixture on top of the biscuit base. Cover and chill for at least 2 hours or overnight until set. Remove the moussecake from the cake tin and scatter the lime shreds around the edge before serving.