Preheat the oven to 200C/400F/Gas 6. Using a heavy, sharp knife or a pair of poultry or kitchen shears, cut the pheasants in half down the back, removing the backbone. Discard the backbone, then chop the pheasants in half down the middle. Trim off any fat or bruised bits.
Place the pheasants in a large bowl. Squeeze over the lemon juice and add the lemon quarters to the bowl. Bruise the rosemary stalks with your hands and add them to the bowl. Season with salt and freshly ground black pepper.
Lightly crush the garlic cloves with the flat side of a knife or with your hands, but don't peel them. Add them to the bowl. Pour over the olive oil and the white wine. Mix well and leave the pheasant to marinate for about 20 minutes.
Heat a heavy-based frying pan (don't add oil).
When the pan is hot, remove the pheasant pieces from the marinade and sear them, skin-side down, to colour. Turn the pieces and brown the other side. Do this in batches so that you don't crowd the pan.
When the pieces are browned, place them in a roasting dish. Pour over the white wine and the marinade from the bowl.
Place the pheasant in the oven and roast for 20-30 minutes, until tender and cooked through (the juices will run clear when the thigh is pierced with a skewer). Remove from the oven and rest for 10-15 minutes.
When rested, cut the pheasant into serving pieces and pile onto a large plate. Pour the pan juices over the top and spoon over the lemon, rosemary and garlic.
Serve with boiled potatoes and a green salad or good bread.