Put the biscuits, cocoa, butter and choc-chips into a food processor and process to a dark, damp sandy consistency. Tip into a fluted tart tin and press into the base and up the sides.

Place in the fridge to chill while you make the filling. Don't forget not to lift it from the base!

Zest the limes and set aside.

Pour the chilled condensed milk into a bowl and add the lime juice.

In a separate bowl, whip the cream until thick. Add the condensed milk and lime and stir until combined. Spread the mixture into the base and sprinkle with lime zest. Refrigerate until the filling is set (about 4 hours but overnight would be best).

Remove the sides from the tin, sprinkle the pie with grated chocolate and serve. Yum