On a low heat, fry the shallots in the duck or goose fat for 6-8 minutes until soft. Leave to cool. In a bowl, mix all the ingredients for the filling except for the rabbit and season well. Cover with cling film and refrigerate until needed.
Preheat the oven to 180C/gas 4. For the pastry, mix the flour with the salt in a bowl and make a well in the centre. Combine the melted lard and water in a saucepan and bring to the boil, then stir into the flour with a wooden spoon to form a smooth dough. Leave the pastry for 5 minutes if too hot to handle.
Line the bottom of a 20cm-wide, 10cm-deep pie ring with a disc of greaseproof paper and grease the tin lightly. Place on a greaseproof paper-lined baking tray. Take two-thirds of the dough and roll into a circle large enough to line the pie ring and with excess to hang over the edges. Carefully press the pastry into the tin, allowing a little to hang over the edge. Carefully fill any tears or breaks – this is important! Roll the remaining pastry into a circle for the lid.
Lay half the filling mix in the pastry case, then lay the rabbit thighs on top, making sure there are no gaps. Season generously and fill the pie with the remaining filling. Brush the edges with the egg and cover with the pastry lid. Carefully crimp the edges to create a seal and trim the edge with a knife. Brush the top of the pie with the beaten egg, make a hole in the middle of the pastry lid and bake for 60–80 minutes.
Remove the ring and brush the sides and top again with egg before baking for a further 15 minutes. Remove from the oven and leave to cool. Once the pie is cold, refrigerate for 2–3 hours.
For the jelly, soak the gelatine leaves in cold water until they soften and squeeze out any water. Heat about a third of the chicken stock in a saucepan and stir in the gelatine until it’s dissolved, then stir into the rest of the stock. Leave to cool, but do not let it set. Once the pie is cold, check around the pastry for any holes and fill them with softened butter so that the jelly doesn’t escape. Pour the stock into the round hole in the top of the pastry until the pie is filled. Cool in fridge until the jelly is set.