Green’s Dictionary of Slang

(US) neat, tidy, perfect; in fig. use, in the image of trad., conservative American values embodied by ‘Mom’s apple-pie’.

1899		W. Raleigh Letter 13 Sept. Letters (1926) I 208: We had an artist in the back room [...] so I could not leave it as apple-pie as I should have liked.
1908		L.W. Payne Jr ‘Word-List From East Alabama’ in DN III:iv 287: apple-pie, adj. Most excellent.
1910		B.L. Bowen ‘Word-List From Western New York’ in DN III:vi 436: apple-pie, adj. Excellent; perfect ‘The house is all cleaned and in apple-pie order’.
1931		Edinburgh Eve. News 3 Oct. 5/5: The phrase ‘apple pie’ I believe to originate from the term ‘cap-a-pie’, that is, ‘from head to foot’.
1958		E. Dundy Dud Avocado (1960) 151: To anyone coming in from the outside [...] wouldn’t we have seemed perfectly OK? Absolutely apple-pie American.
1972		Sat. Rev. (US) 17 June 50: Could the Cuban vision of life, as reflected in these films, be so appealing that it would corrupt and endanger apple-pie America?
1988		(con. 1940s) C. Bram Hold Tight (1990) 75: Everybody looked so clean and wholesome and apple-pie good.
1991		P. Cornwell Body of Evidence (1992) 310: They still lie to you, tuck the animal in bed and spoon-feed him chicken soup like he’s Mr. Apple Pie America.
1999		Guardian Guide 28 Aug.–3 Sept. 59: Just when it all looks a bit too weird, apple-pie values are restored.
1999		Observer 15 Aug. 23: Gore’s apple-pie marriage makes them yawn.
2002		D.H. Sterry Chicken (2003) 131: I need to [...] drink a few beers, maybe even have some old-fashioned American apple-pie sex.