Heat the oven to 200°C. Bring a large pan of salted water to the boil. Boil the potatoes until almost cooked but still firm. Drain and allow to cool a bit. Heat the goose fat and olive oil in a roasting tin, while you cut the potatoes in half lengthwise.
Put them into the hot fat with the whole cloves of garlic, the rosemary, bay leaves and thyme. Jumble the potatoes round in the fat un