Pre-heat the oven to 220°C/Gas 7.
Season the partridges inside and out with salt and pepper and rub with butter. Place the birds in a roasting tray, in which they fit snugly, and cook for 15 minutes, basting every so often.
Around halfway through cooking, bring a pan of lightly salted water to the boil and cook the greens for about 6–7 minutes until tender, then drain.
Meanwhile, heat a little more butter in a frying pan and cook the mushrooms over a medium heat for a few minutes, seasoning halfway through cooking.