John Gill Commentary 2 Samuel 13:6

"So Amnon lay down, and feigned himself sick: and when the king was come to see him, Amnon said unto the king, Let her sister Tamar come, I pray thee, and make me a couple of cakes in my sight, that I may eat from her hand." — 2 Samuel 13:6 (ASV)

So Amnon lay down, and made himself sick
Took the advice of his cousin Jonadab, and acted according to it:

and when the king was come to see him ;
as he quickly did, after he had heard of his illness:

Amnon said unto the king ;
who perhaps inquired of his appetite, whether he could eat anything, and what:

I pray thee let my sister Tamar come ;
he calls her sister, as Jonadab had directed, the more to blind his design; though it is much that so sagacious a man as David was had not seen through it; but the notion he had of his being really ill, and the near relation between him and Tamar, forbad his entertaining the least suspicion of that kind:

and make me a couple of cakes in my sight ;
heart cakes, as the word may be thought to signify; called so either from the form of them, such as We have with us, or from the effect of them, comforting and refreshing the heart:

that I may eat at her hand ;
both what is made by her hand, and received from it.