Wash the turkey leg and pat dry, pepper and salt. Then rub the mustard all over the meat. Wash the thyme stalks, shake dry and distribute them in a large enough roasting pan so that the turkey leg covers the stalks.
Cook in the oven at 160 degrees for at least 3 1/2 hours.
Remove the meat and wrap it in aluminum foil. Mix the stock with the cream or sour cream, bring to the boil and serve.
Hearty side dishes like dumplings, red cabbage or potatoes go well with it.