Preheat the oven to 200°C / 400°F / Gas mark 6.
Remove all the fat from inside the bird and use a skewer to prick the goose skin all over, especially under the wings.
Dry with kitchen paper, then leave for 1 hour to dry completely.
Season the goose cavity with salt and pepper and stuff with the oranges, bay leaves and the thyme.
Rub the breast and legs with 2 tablespoons of oil and season generously with salt.
Lay the carrots in the middle of a very large roasting tin.
Rest the bird on top of the carrots.
Using a large bowl, toss the parsnips and turnips with the rest of the oil and bay leaves, then scatter around the goose.
Cover the tin with a large piece of foil, making sure it seals tightly.
Place the goose in the oven for 1½ hours.
Take the goose out of the oven.
Remove the foil and carefully use a baster to remove the fat juices from the tin and reserve in a bowl.
Lightly baste the goose and turn the parsnips.
Re-cover with foil and roast for another 1½ hours.
Remove the juices from the pan again and baste, then increase the heat to to 220°C / 425°F / Gas mark 7.
Return to the oven without any foil to brown for a final 30-40 minutes until golden brown.
Remove the goose from the oven and transfer to a large platter to rest in a warm place for 30 minutes.
Scoop the vegetables out into another roasting tin and keep warm in a low oven.
Save the goose tin to finish making the gravy in.
To make the gravy, remove the oranges from the goose using a fork or tongs.
Pour off all the fat from the roasting tin into a bowl.
Scatter the sugar into the tin and stir to scrape off any brown bits.
Add in the vinegar, simmer until nearly dry, then stir in the jelly.
Allow to bubble and cook down. Last, add the stock and squeeze in the juice from the oranges.
Bring everything to the boil, then strain into a jug or small saucepan to reheat later.
In a bowl, toss the pears in the icing sugar until completely coated.
Serve the slow-roasted vegetables in a separate bowl and the gravy.