“heartcakes.” The Hebrew is labiybah (#03834 לָבִיבָה), and according to the Holladay Hebrew and Aramaic Lexicon and Everett Fox (The Schocken Bible: The Early Prophets) the meaning is not just “cakes,” but heart-shaped cakes. Fox writes: “…others [have] simply ‘cakes,’ but the ‘heart’ (Heb. leiv, leivav) motif is central to the Avshalom [sic] stories, as I have argued…. Shaped foods were known in the ancient Near East.” Fox goes on: Amnon “pretends to be ill and requests that his half-sister make levivot, usually translated as ‘cakes,’ for him. …But as some interpreters have noticed, the homonym (levav) means ‘heart,’ and the verbal form of l-b-b (the biblical v and b are the same letter) occurs in the Song of Songs 4:9, ‘You have captured my heart’ (NJPS). So a word connected in love poetry with seduction is appropriate enough in the mouth of the lovesick Amnon, and on this and other grounds…we are justified in understanding levivot as something like ‘heartcakes.’”
Since Amnon would have had many people who could cook for him, it may have made more sense to David that Amnon asked for “heartcakes” specifically from Tamar, who may have been known for cooking them. In fact, it is possible that Tamar even brought her own pan to cook them in (see commentary on 2 Sam. 13:9, “pan”).