Put the lamb, cornflour, cumin, nutmeg, salt and pepper into a large foodsafe plastic bag and shake until the lamb is evenly coated.
Heat a large heatproof casserole dish on a high heat, add the oil, then brown the meat in small batches and set aside.
In the same dish, add the onions, carrots, parsnips and tomato purée and soften for 3-5 minutes with the lid on, stirring occasionally. Deglaze the pan with wine and port, stir, and add the meat, stock and jelly. Bring to the boil and cover. Transfer to the oven for about 2 hours, or until the meat starts to fall apart.
Remove from the oven and place on top of the hob. Remove the lamb with a slotted spoon and put into a pie dish. Simmer until the sauce has thickened, then add the sauce to the pie dish, stirring to coat the lamb, and set aside to cool for at least an hour – longer if possible.
30 minutes before you’re ready to eat, preheat your oven to 200ºC/Fan180ºC/Gas 6.
Cover the pie dish with puff pastry, crimp the edges to seal, brush the pastry with egg yolk and cut two slits in the top of the pie to let the steam escape.
Place on a baking tray in your preheated oven for 20-25 minutes until the filling is hot and the pastry is crisp and golden. Remove from oven and allow to rest for 5 minutes before serving.