1. Place the biscuits in a food processor and pulse until they are crushed but not too fine. Tip into a bowl, add the melted butter, stir to combine.
2. Press into the base of a 20cm tin. Push up the sides of the tin to create a crust. Place in the fridge to set. Pre heat your oven to 150°C/Gas Mark 2.
3. To make the filling, whisk the egg yolks with the condensed milk. Add the lime juice and zest and whisk again. Pour into the prepared base.
4. Bake for 25-30 minutes or until just set. The filling will have risen and may have started to colour around the edges.
5. Remove from the oven and leave to cool at room temperature. Chill in the fridge for at least 2 hours before serving.
6. Serve a wedge of cooled pie with cream and a little more lime zest.