This is a new cut for us! So with no personal experience with cooking it I’ll refer to the Nose-To-Tail App for some information.. Enjoy!
“Beef Spleen is another one of the underrated Beef offal parts, which are fit for consumption but not as popular among the consumers. Having a texture similar to the Liver, the Spleen can add a novel flavor to any dish of which it is a part. It is also a very nutritious Beef organ.
Much like the Liver, Spleen can be used as a stuffing for sausages as well as dishes like pate. It can be marinated first and then roasted. Since Spleen can be a tough portion, it is sometimes preferred to cook it using slow, moist cooking methods like stewing and braising. Many cooks suggest making a fine paste of the Spleen and using it as a dip. It is advisable to first douse the Spleen in a bath of acidic water or buttermilk so that it lightens up on flavor as well as smell.
In the steer's body, the Spleen is located adjacent to the rumen.
Spleen's origin goes back to the 1300s, with its roots found in Old French (esplen), Latin (splen) and Greek (splen).
Although high in cholesterol, Beef Spleen is rich in iron and protein with little sodium content.”