To make the jelly, soak the gelatine in water for 5 minutes and heat the stock until hot but not boiling. Remove the gelatine from the water and squeeze out any excess liquid, then stir into the stock to dissolve it. Cool to room temperature. Using a funnel, carefully pour the jelly bit by bit into the steam hole of the pie, waiting for a few seconds before each addition. If the liquid leaks from the bottom of the pie, chill it for 15 minutes for the jelly to seal the hole, then add the rest. Put the pie into the fridge to set overnight. Release from the tin to serve.