E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The lions or crack men of the day. The phrase was first used in Sam Slick. The upper crust was at one time the part of the loaf placed before the most honoured guests. Thus, in Wynkyn de Wordes Boke of Keruinge (carving) we have these directions: Then take a lofe in your lyfte hande, and pare ye lofe rounde about; then cut the ouer-cruste to your souerayne Furnwall, in Manners and Meales, etc., says the same thingKutt the vpper cruste for your souerayne.
I want you to see Peel, Stanley, Graham, Shiel, Russell, Macaulay, old Joe, and so on. They are all upper crust here.