This section is from the book "Cooking For Profit", by Jessup Whitehead. Also available from Amazon: Cooking for Profit.
It is the making of sweetbreads to press them to a flat shape between two pans after boiling them, and let them get cold that way. As a rule they are always boiled before being otherwise cooked; not but what they may be cut up and stewed, or split open and broiled without brevious cooking if they are i calves' sweetbreads, and tender, still it is best to do the other way and the largest and finest that people will naturally select for the best are the very ones that need about an hour's boiling to make them tender.
Sweetbreads are the whitish pieces of soft meat that look like fat, found near the throat and the heart of the animal the largest coming from the heart. They are used extensively as a fancy meat for little side dishes.
When they first come from the butcher's put them in cold water and after steeping a while set them over the fire in a saucepan of water to cook for an hour. As they have an insipid taste that is not improved by keeping, a little vinegar should be put in the water they are boiled in - about four tablespoons - and some salt. Take them up in a pan or dish, put another on top of them and a heavy weight like a pail of water on that. When cold you can split them into thin slices and trim off the rough edges.
 
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