Cooked Prime Meat is produced by cooking Raw Prime Meat and is used as a food source, a taming food, and as an ingredient in many of the Rockwell Recipes. The trick with Prime Meat is that is spoils incredibly fast, so knowing how to cook it fast and preserve it are key to building a supply of this resource.
Until you reach higher levels, your only way to cook Prime Meat fast enough to avoid losing too much of it is to have one campfire for each one to two pieces of Raw Prime Meat. When it is raw, this stuff spoils in two minutes. Once cooked, you have 40 minutes before it will spoil. The only other option for cooking it is to use the Industrial Grill, which is a higher level Engram and requires a good amount of resources and Gasoline.