One's not sincere, on reflection, in thanks for snack (5,3)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

A confection of coconut and dried fruit. One’s not sincere gives I’M LIAR, which is reversed (on reflection) withing TX for thanks – perhaps the thin end of the wedge of the Sign of the Times setting up camp in our hallowed fogeydom.