A popular cookie pun is:
 
Q: Why did the cookie cry?
A: Because his mother was a wafer so long (away for so long).
   
“I call my baby ‘Nabisco’ because he’s been a wafer so long” was cited in 1927. The joke went viral in 1939-40. “Do you, students, know why the little cookie was crying? Because his mother was a wafer so long” was cited in December 1939.
   
   
7 December 1927, The Daily Northwestern (Evanston, IL), “Acorns,” pg. 2, col. 2:
SODA I.
I call my baby “Nabisco” because he’s been a wafer so long.
Sunny
 
6 December 1939, The Coe College Cosmos (Cedar Rapids, IA), pg. 2, col. 1:
Do you, students, know why the little cookie was crying? Because his mother was a wafer so long.
 
19 January 1940, Iola (KS) Register, “Juco Notes” by Shirley Drake, The Lampoon, pg. 2, col. 6:
The little cookie was awfully sad because his mother had been a wafer so long.
 
21 January 1940, Amarillo (TX) Sunday News and Globe, “Over the Fences” by Evelyn Boyd, sec. 2, pg. 3, col. 3:
TO END ALL PUNS
Did you hear the plight of the little cookie that fell out of the box?
 
He just cried and cried because his mother had been a wafer so long.
 
Old Fulton NY Post Cards
19 December 1940 Washington County Post (North White Creek, NY), “Do Y’Know,” The Orange Tattler, pg. 10, col. 5:
Why were the two little cookies so sad? Because their mother was a wafer so long.
 
14 January 1949, San Luis Obispo (CA) Telegram-Tribune, “My Man” by Margene, pg. 3, col. 1:
“Do they call her ‘Cookie” because she’s been a WAFER so long?”
 
7 January 1950, Chicago (IL) Daily Tribune, “In the WAKE of the NEWS” by Arch Ward, pt. 2, pg. 1, col. 2:
D’ya think it’s fair, Arch—my girl friend calls me Cookie because I’ve been a wafer so long?
—Salt Water Sailor
 
15 December 1962, Boston (MA) Globe, “Around And About” by Jerry Nason, pg. 13, col. 1:
HERE AND THERE—Morrie Gallant, “They call veteran Buffalo Bills’ fullback Gilchrist ‘Cookie’ because he’s been a wafer so long.”
 
Google News Archive
1 February 1966, The Free Lance-Star )Fredericksburg, VA), “Fun Time—The Riddle Box,” pg. 11, col. 2:
Why did the cookies cry?
Because their parents had been a wafer so long.
 
Google Books
December 1977, Boys’ Life, “Think & Grin,” pg. 82, col. 3:
Izzy: Why was the baby cookie sad?
Dizzy: Because his mother was a wafer so long.—Mike Souveroff, Baldwin, N.Y.
 
Google News Archive
“Jokes, gags reflect our society” by Ben Sherwood (Los Angeles Times),
WASHINGTON—“Why didn’t the baby cookie ever stop crying?”
 
“Because its mother had been a wafer so long.”
   
Google Books 
The Mammoth Book of One-Liners
By Geoff Tibballs
London: Constable & Robinson
2012
Pg. ?:
Why did the biscuit cry?
Because his dad had been a wafer so long.
 
Google Books
The VERY Embarrassing Book of Dad Jokes:
Because your dad thinks he’s hilarious
By Ian Allen
London: Portico Books
2012
Pg. ?:
Why did the baby biscuit cry?
Because its mother had been a wafer so long.
 
Twitter
anti joke apple
‏@antijokeapple
Why did the cookie cry?
Because his mother was a wafer so long.
11:17 PM - 4 Mar 2013
 
YouTube
Jokes - Why did the cookie cry? Because his mother was a wafer so long!
jokesus
Published on Oct 5, 2015
Joke :
Why did the cookie cry?
Because his mother was a wafer so long!