Sift flour into a bowl and add salt and sugar. Cut butter into flour with a pastry cutter until mixture resembles fine breadcrumbs. Make a small well in the centre and add egg and lime juice.
Mix into a firm dough. Wrap the pastry in a plastic bag, then chill for 25-30 minutes.
Roll out pastry between two sheets of plastic wrap.
Cut small rounds and fit into lightly-greased tart moulds.
Trim and neaten the edges. Prick the base with a fork and chill in the refrigerator for 10-15 minutes. Bake in preheated oven at 180°C for 10-12 minutes. Remove and set aside.
To prepare the filling
Beat cream cheese, sugar and butter until light and creamy. Add in egg and continue to beat until well blended. Mix in whipping cream and rum (optional). Sift in flour and stir in half portion of crushed Oreo cookies to mix.
Spoon a heaped tablespoon of filling into the prepared pastry cases. Sprinkle with remaining crushed Oreo cookies.
Bake in preheated oven at 200°C for 15 minutes or until cooked through. Serve immediately.