For the pastry, blend the flour, baking powder, salt, butter and lard in a food processor until the mixture resembles breadcrumbs. Gradually add the water in a thin stream and continue to blend until the mixture starts to come together as a dough. Wrap the dough in cling film and chill in the fridge for at least an hour.
Meanwhile, for the cranberry topping, bring a pan of water to the boil, then turn down the heat to a simmer. Add the cranberries and kumquats and simmer for 8-10 minutes, or until the fruit has broken down. Add the sugar, allspice and cinnamon stick. Stir until the sugar has dissolved, then simmer for a further 8-10 minutes. Add the port, return the mixture to the boil for 2-3 minutes, then remove from the heat. Stir the softened gelatine leaves into the cranberry mixture until well combined, then set aside to cool. When the cranberry topping has cooled, chill in the fridge until set.
To cook the pastry, preheat the oven to 170C/325F/Gas Grease a 23cm/9in springform tart case with butter. Line the base with a disc of baking parchment. Turn the pastry out onto a lightly floured work surface and roll out until it is 4cm larger in diameter than the tin. Line the tart case with the pastry and press down until the pastry case is the same shape as the tin. Cover the pastry with greaseproof paper and fill with baking beans. Transfer to the oven and bake for 15-20 minutes.
Remove the baking beans and greaseproof paper and trim the edges of the pastry. Set the pastry case aside to cool.
For the tart filling, heat the olive oil and butter in a large frying pan over a medium heat. Add the onion, leek and celery and fry for 4-5 minutes, or until softened. Add the flour and stock and bring to the boil. Reduce the heat to a simmer and simmer the mixture for 4-5 minutes, or until the stock has thickened.
Add the cream and simmer for 2-3 minutes, or until warmed through, then add the mustard powder and parsley and stir until well combined. Add the gammon and turkey pieces and stir until well combined. Season, to taste, with salt and freshly ground black pepper. Spoon the tart filling into the pastry case, then transfer to the oven and bake for 15-20 minutes. Remove from the oven and set aside to cool.
While the pie is cooling, spread the cranberry jelly over the top.
When the pie has completely cooled, cut it into slices and divide the slices equally among the serving plates. Serve with a green salad and crisps.