The DA has "pie" meaning "something quite easy, a treat, a cinch, also
_easy as pie_," from 1889. It's a sporting quote from OUTING.
This is from SPORTING LIFE, 26 May 1886, pg. 8, col. 1:
LATHAM's base-running is said to be simply wonderful. He has several
times ran in from third with the catcher under the bat. As for stealing
second and third, it's like eating pie.
This is from SPORTING LIFE, 15 September 1886, pg. 5, col. 3:
THE St. Louis Maroons are no longer "pie" for the other League clubs. It
takes hard work to down them now.
The RHHDAS has the similar "piece of cake" from 1936 and "cake" from
1911, but I also have an 1886 "cake" somewhere near my "pie."
Notice that it's EATING pie, not BAKING pie--which might not be easy.
Actually, eating pie might not be easy, either. Say you're in Houlihan's, and
someone offers you the apple pie...