Turn a metal muffin or bun tin upside down. Divide the cookie dough into 12 pieces. Roll each piece into a ball, then press over each dome, shaping down the sides to make an upside-down tart case. Chill for 30 mins.
Heat oven to 180C/160C fan/gas 4. Bake the tin and cookie dough for 12-15 mins until the tart cases are golden. While still warm, cut away any excess that has dripped down the sides, prying with a knife to remove. Cool on a wire rack.
Whip the cream to soft peaks, then stir in the cream cheese and icing sugar. Drain the mandarins, reserving the juice. Add 4 tbsp of mandarin juice to the cream mixture and beat until smooth. Spoon into the cases and top with slices of mandarin. Chill until ready to serve.