Preheat the oven to 210C/410F/Gas 6.
For the pheasant, remove the legs and wishbone of the pheasant. Season thoroughly inside and out with salt and freshly ground black pepper. Reserve the legs for use in another dish.
Heat a frying pan until hot, add the butter, place the pheasant in the pan and sear on each side until golden.
Place in the oven for about 10-15 minutes, or until cooked to your liking. Remove from the oven and rest.
For the parsnips and chestnuts, place the parsnips, sherry, sugar and butter into an earthenware dish or roasting tin and mix together to combine.
Place in the oven for 15-20 minutes until golden and tender.
Remove and place on the hob, bring to a simmer then reduce the liquid down to a thick glaze. Add the chestnuts and parsley and mix together. Season with salt and freshly ground black pepper.
To serve, carve the breast from the pheasant. Place the parsnips and chestnuts onto the centre of each serving plate. Top with the pheasant and a handful of watercress.