In a steam-heated cooking vessel having a double shell surrounding the food container, in which water vapour is produced via a heated water bath, the valve (6) serving for venting the double shell is attached closely above the level of the water bath. In this manner, the heating-up operation is reduced to the shortest time without appreciable amounts of water vapour escaping. In a condenser connected downstream of the valve, any condensation occurring is automatically returned into the vapour space. <IMAGE>