Preheat the oven to 200°C.
Place 25g of butter, salt, pepper, a bacon rasher, and a bay leaf inside each pheasant.
Place the onion, mushrooms, carrot, leek, garlic, and thyme in a roasting tin and set the birds on top.
Spread the remaining butter over the pheasants and roast for 45 minutes.
Fry bacon lardons in oil until crisp and remove from the pan.
Cook the leek and celeriac in the pan for 8 minutes before returning the bacon and adding cider.
Simmer until liquid reduces by half, then add stock and reduce by half again.
Stir in the cream and thyme leaves and season with pepper.
Serve the carved pheasant with the roasted vegetables and the creamy bacon and celeriac sauce.