Preheat the oven to 200°C.
Separate pheasant breasts and legs, then chop carcasses into pieces.
Roast legs, carcasses, onion, tomatoes, and herbs for 15 minutes.
Boil roasted components in water, simmer for 45 minutes, strain, and reserve stock.
Season pheasant breasts and sear in a hot pan with olive oil for 2 minutes per side.
Roast breasts in the oven for 10-12 minutes and rest for 5 minutes.
Deglaze the pan with red wine and reduce by half.
Add stock to the pan and simmer until the sauce thickens.
Roast pierced chestnuts for 20-25 minutes, then peel and chop.
Boil potatoes until tender, drain, and mash with olive oil, chestnuts, and parsley.
Toss parsnips with sherry and honey, and roast for 20 minutes until golden.
Serve sliced pheasant over mash with parsnips and sauce.