Parboil a pair of sweetbreads, adding to the boiling, salted water the onion, bay leaf and mace. Cool and cut into cubes.
Soak the gelatine in cold water a few minutes, add the boiling water, and stir until dissolved. Let stand to slightly harden. Rinse a ring or other mould in very cold water, place a few spoonfuls in bottom of mould, add a layer