Take the guinea fowl out of the fridge 30 minutes before cooking so it roasts evenly. Pat the skin completely dry with paper towels.

Heat the oven to 200C/400F. Chop the pancetta and sage finely, then mash together with the softened butter, half the crushed garlic, and a pinch of salt and pepper to make a compound butter.

Loosen the skin over the breast and thighs with your fingers, then push the pancetta butter underneath, spreading it evenly. Rub any leftover butter over the outside skin.

Season the cavity with salt, then stuff with the lemon halves, remaining garlic, and rosemary sprigs. Tie the legs together with kitchen twine.

Scatter the onion, carrots, and celery in the base of a 30 x 23 cm / 12 x 9-inch roasting pan, drizzle with olive oil, and set the guinea fowl on top, breast side up.

Roast at 200C/400F for 20 minutes to color the skin, then lower the oven to 180C/355F and continue roasting for 50 to 60 minutes, basting with pan juices every 20 minutes.

Check doneness with an instant-read thermometer inserted into the thickest part of the thigh, it should read 165F/74C, and the juices should run clear, not pink.

Transfer the guinea fowl to a board, tent loosely with foil, and rest for 10 minutes before carving.

Meanwhile, pour off excess fat from the roasting pan, set it over medium heat on the stovetop, and pour in the white wine, scraping up the browned bits.

Simmer the wine for 2 to 3 minutes until reduced by half, then add the chicken stock and simmer for another 5 minutes until slightly thickened. Strain into a small saucepan and season to taste.

Carve the guinea fowl into portions and spoon the pan sauce over the top before serving.