Veggie Christmas pie

Preheat the oven to 200ºC, gas mark 6. Grease a deep, 18cm loose-bottomed cake tin with a little oil. Toss the diced celeriac and parsnip in a little olive oil, season and spread out on a parchment-lined baking tray. Roast for 20 minutes until golden and tender.

Meanwhile, in a large frying pan over a low heat, sauté the leeks in the butter with the thyme and some salt and pepper, for about 10-12 minutes, until soft. Tip the cooked leeks into a large bowl, add the roasted vegetables, and mix well with the rest of the filling ingredients, excluding the eggs and cranberry sauce. Leave to cool for 20 minutes then add the beaten eggs.

Meanwhile, make the pastry. Mix together the flour, salt and 2 of the beaten eggs in a very large mixing bowl with a metal spoon. Place the butter and 180ml water in a saucepan and heat until the butter has melted and the mixture just comes to the boil. Quickly beat it into the flour mixture, with a spatula, a little at a time until it has all been combined and the mixture is smooth. It will be quite soft. Shape into a ball, wrap and refrigerate for 10 minutes until it has cooled a little.

Knead the pastry briefly, then cut off and set aside 350g (for the lid and decorations). Roll the remainder into a ball then roll out on a lightly floured surface until 0.5cm thick and at least 35cm diameter. Carefully lift it into the tin, easing it into the corners. Use a knuckle to gently press the pastry into the edges. Trim off the excess pastry, leaving 1cm hanging over the edge of the tin.

Spoon the filling into the pastry-lined tin and gently press it down. Spoon the cranberry sauce evenly over the surface of the filling. Brush the exposed pastry rim with the remaining beaten egg. Roll out the remaining pastry to 3mm thick then cut out a circle 1cm wider than the tin. Place the pastry over the top of the pie and press the edges together to seal, then crimp between your thumb and forefingers. Cut a small cross in the middle to let steam escape.

Re-roll any leftover pastry and trimmings then cut out decorative shapes with a pastry cutter. Brush each shape with a little beaten egg then arrange them on top of the pie. Brush the whole of the top of the pie with beaten egg. Put the remaining beaten egg to one side as you will need it to glaze the finished pie.

Bake for 20 minutes, then cover the top with foil and cook for a further hour, or until piping hot throughout and a metal skewer inserted into the centre feels hot to the touch. Leave the pie to cool in the tin for 10 minutes before carefully unmoulding it. Brush the sides with beaten egg and place it back on a baking tray. Return to the oven for 5-10 minutes (keeping the top covered with foil if the top looks dark) until golden and shiny all over.