The expression “to eat humble pie”, meaning to humble oneself, to apologize or abase oneself profoundly, was originally a play upon words, a jocular substitution of humble for umble wherein the meaning of humble was retained.
Umble pie was, and maybe still is in some parts of England, a pasty made of the edible inward parts of an animal, usually a deer.
The umbles were considered a delicacy by most persons, although some thought them to be fit only for menials. And the pie made of those parts was also variously appreciated; it graced some tables, but James Russell Lowell, in 1864, said, “Disguise it as you will, flavor it as you will, call it what you will, umble-pie is umble-pie, and nothing else.”
Etymologically the phrase is interesting; though in present use it is humble pie, jocularly derived from umble pie, umble is one of a number of English words which originally had an initial “n.” Thus, just as apron was originally napron, adder (the snake) originally nadder, so umble was originally numble.
But there would have been no point to the joke then, without an initial vowel to which cockney “h” might be prefixed.