As easy as pie is a popular colloquial idiom which is used to describe a task or experience as pleasurable and simple. The idiom does not refer to the making of a pie, but rather to the act of consuming a pie ("as easy as eating a pie") which is usually a simple and pleasurable experience. The phrase is often interchanged with piece of cake, which shares the same connotation.
Origin
There are some claims that the phrase originated in the 1920s from the Indigenous New Zealand expression "pie at" or "pie on" from the Maori term "pai" which means "good", but it was used in the Saturday Evening Post of 22 February 1913, and in 1910 by Zane Grey in "The Young Forester," and is probably a development of the phrase "like eating pie," first recorded in "Sporting Life" in 1886.