Use a small sharp knife to score the skin of the duck. Be careful not to cut through to the flesh. Place the duck into a large baking tray or cast iron pot. Stuff ½ onion, 2 garlic cloves and 1 sprig of thyme into the duck cavity. Then place the remaining onion, garlic and thyme around the duck. Season with salt and then pour over the wine.
Cook in the oven for 1 hour. Remove and place the potatoes and carrots around the duck. Return to the oven and cook for a further 1 hour.
Remove and let the duck rest for 5-10 minutes before serving.