Lesley McCullough, who alerted NOOBs to “happy-clappy,” has a new hyphenated expression on her mind. She writes:
While reading a review in New York Magazine of “Six Minutes to Midnight” a new film written and starring Eddie Izzard, I noticed that the writer Helen Shaw referred to a performance by James D’Arcy as follows: “In D’Arcy’s case, he has chosen a wildly over-egged delivery, slicing each word onto the plate as though he’s serving Christmas ham.” I have always thought of “over-egged” as a particularly UK compound adjective derived from the idea of an over egged pudding being too rich and fluffy.
As with “happy-clappy,” I had no familiarity with “over-egged.” The OED confirms Lesley’s sense, defining the verb form, “over-egg,” as: “To embellish or supply to excess. Chiefly in to overegg the pudding: to go too far in exaggerating, embellishing, or doing something.” The first citation, from the 1845 book Hillingdon Hall, helpfully gives information on the term’s origin: “‘We mustn’t over-egg the pudding,’ as the Yorkshire farmers say.” It and all subsequent cites are from British sources. Interestingly, only the most recent one, from the Evening Standard in 2002, leaves out “pudding.” (“The bank was anxious however, not to overegg investor expectations for the current year.”)
The first time the expression appeared in the New York Times (other than written by or quoting British people) was in William Safire’s language column in 2003, in which Safire reported being asked about it and admitted never having heard it. The next time was in 2007, by the writer Paul Theroux, who is an honorary Englishmen. But then it showed up twice in 2020: in a film critic’s judgment of the 2020 film Fire Saga that “this over-egged farce whips slapstick and cheese into an authentic soufflé of tastelessness,” and in a book reviewer’s judgment that in a biography of Ted Kennedy, “scenes are often over-egged.” Both those writers are American.
As is Helen Shaw, whose review prompted Lesley to write. Or at least she went to Harvard.
notoneoffbritishisms.com 
I suspect the presence, or absence, of the pudding might be a regional distinction. Once inside the M25 I think one generally just “over eggs”.
Andy mentions the M25, for those folk who don’t know what he refers to it’s the highway that surrounds London, like the Beltway in Washington DC.
There is also the phrase ‘to egg someone on’, meaning to incite. I have no idea where that one derives from, or whether it’s connected to ‘over-egging’.
I’d say egg is a Scandinavian homonym – there’s egg meaning edge, where I guess the idiom to egg on comes from – and then there’s egg meaning, well, egg. One is sharpish while the other is, thankfully, not 🙂
To “egg someone one” is common in US, by the way, as is (though a bit old-fashioned) “a good egg” meaning a good person.
“Egg on” comes from “edge” — or rather, from the Norse word “egg” that we borrowed and eventually turned into “edge”. It implies goading someone into action at knifepoint.
If the pudding comes from Yorkshire, I expect it was originally Yorkshire pudding, which traditionally accompanies roast beef at Sunday lunch. The nearest equivalent to Yorkshire pudding in America looks like popovers, for which Julia Child recommends 3 eggs, not 4. https://myyellowfarmhouse.com/tag/julia-childs-popover-recipe/
I agree – too many eggs in a Yorkshire pudding batter makes it stodgy and claggy, and will prevent it from rising well.
Fascinating! I don’t recall hearing this phrase before, but it strikes me that, in addition to the evolved association with exaggeration, or ruining by overdoing, it may have its origin in a more subtle expression of waste. For farmers, eggs are a measure of wealth (and insecurity), with market prices rising and falling. I just finished reading Sinclair Lewis’s Main Street, and recall how the self-righteous Mrs. Bogart berates the teacher she boards, Fern Mullins: “My lady must have two eggs every morning for breakfast, and eggs sixty cents a dozen, and wa’n’t satisfied with one, like most folks — what did she care how much they cost or if a person couldn’t make hardly nothing on her board and room, in fact I just took her in out of charity and I might have known from the kind of stockings and clothes that she sneaked into my house in her trunk…”