Cook in the oven for 30 mins then reduce the heat to 160C/140C fan/gas 3 and cook for 90 minutes. Brush the top with beaten egg and return to the oven for a further 20 mins. Leave until cold. Soak the gelatine in cold water for about 5 mins, then remove and squeeze out the excess water. Heat the stock until almost boiling. Remove from the heat and stir in the gelatine. Leave to cool to room temperature. Use a small funnel to pour the stock into the pie through the hole in the top. Pour in a little at a time allowing a few seconds before each addition. Place in the fridge to set overnight.
