In a large flameproof casserole, soften the onion in the oil gently over a low to medium heat for about 10 minutes. Add the sauerkraut and the carrots, toss together well, then add the juniper berries. Stir in the stock and simmer covered for 1 1/2 hours. Add a little water if necessary to keep the mixture moist during cooking. Add the sausages just before serving, mix well, and serve with a big bowl of mashed potatoes.