Peel and dice two large turnips and two carrots; halve lengthways and slice two leeks; slice about 250g mushrooms; finely dice three rashers of bacon; cut around 4-5 pheasant breasts (or 2-3 chicken breasts) into roughly 1cm cubes.
Saute leeks, turnips and carrots in a little olive oil, then add a good slug of white wine and about half a litre of hot chicken stock, and add a sprig of thyme. Cook with a loose lid until the turnips are soft. Put cooked veg into baking dish, save the cooking liquid, and wipe out the pan. Add the pheasant, sauté until partly cooked, then add mushrooms and bacon and continue to sauté until the pheasant pieces are cooked and the mushrooms are softened. Transfer solids to baking tray with other veg, and once again save the liquid with the first round of cooking liquid. Stir the veg and meat well to combine; add a cupful of frozen peas if you wish at this point.
Next, use the reserved cooking liquid to make a veloute sauce – make a roux with butter and flour, slowly add the cooking liquid (adding extra hot water if required) whisking to avoid lumps. When all the liquid is incorporated, remove from heat and add a good dash of cream. The sauce should be thick enough to coat the back of a spoon, but not claggy – if it’s not loose enough, add extra hot water before removing from the heat. Add to the meat and veg, and once again stir well to coat.
Boil three large peeled potatoes, and a trimmed celeriac bulb; mash with butter, salt, pepper, and enough milk to loosen the mixture a little. Allow to cool until you can comfortably stick your finger in it to taste, then whisk in two eggs. Spread the mixture over the pie filling, and top with plenty of grated cheese. Cook in a hot (200c) oven until the top is browned and well set.