1. Preheat the oven. Spray a 22cm cake tin with non-stick cooking spray and cover the outside with foil; this prevents the filling from leaking out or water seeping in while it’s in the water bath.
2. Crumble the biscuits and mix with the melted butter. Press the biscuits into the bottom of the cake tin to form a crust and place in the fridge until the filling is ready.