1.Grease a 14cm x 22cm loaf pan; line base and sides with two layers of foil, extending the foil 10cm over edge of pan.
2.Blend or process biscuits until they become fine crumbs; transfer to a medium bowl. Stir in nuts and butter until combined. Using your hands, press biscuit mixture lightly over base of pan. Cover; freeze 20 minutes or until firm.
3.Meanwhile, slice cheeks from mangoes; discard skin and seed. Blend or process mango, sugar and juice until smooth. Transfer to a medium bowl.
4.Blend or process ricotta and extra sugar until smooth. Add sour cream; blend or process until just combined.
5.Drop alternate spoonfuls of mango mixture and ricotta mixture over biscuit base in pan; using a butter knife, gently swirl the mixtures. Cover; freeze overnight or until firm.
6.Turn frozen mixture out of the pan onto a platter or board; remove foil lining. Decorate with extra mango slices and lime. Stand 15 minutes before serving.
Instead of brandy snaps, you could use ginger snap, butternut snap or honey snap biscuits.Note