Spleen

spleen (or melt or milt), a spongy organ found near the stomach or intestine of most vertebrates, which has the function of maintaining blood in good condition. Jane Grigson (1967) describes it thus:

In appearance it is a long flat oval of dark reddish meat, with a line of white fat running from end to end. It usually disappears—in England, as in France—with the rest of the pluck [heart, liver, lungs] into faggots, sausages and pâtés.

Although that sums it up well, the spleen may also appear in mixed offal dishes and occasionally has a lead role, as in an interesting street food of Palermo in Sicily, guastelle (spleen sandwiches) of which Sokolov wrote in a 1994 issue of the Natural History Magazine:

Guastella is actually the name for a certain kind of soft roll with sesame seeds on top; it resembles a hamburger bun. You cut it in half and fill it with warmed ricotta, caciocavallo [a hard cheese made from cow’s milk], and beef spleen, an organ meat that is much appreciated in Sicily. The spleen is sliced and cooked literally swimming in lard.