“If you mix butter and flour, you’ll roux the day”

“Roux” (a mixture of flour and fat) has resulted in many “roux the day” (roux + rue the day) puns. “Roux the day” has been cited in print since at least 1989, when it was used in a headline in the Chicago (IL) Sun-Times.
 
     
Wikipedia: Roux
Roux (/ˈruː/) is flour and fat cooked together and used to thicken sauces. Roux is typically made from equal parts of flour and fat by weight. The flour is added to hot oil on the stove top, blended until smooth, and cooked to the desired level of brownness. Clarified butter, vegetable oils, bacon drippings or lard are commonly used fats. Roux is used as a thickening agent for gravy, sauces, soups and stews. It provides the base for a dish, and other ingredients are added after the roux is complete.
 
Wiktionary: rue the day
Verb
rue the day
(third-person singular simple present rues the day, present participle ruing the day, simple past and past participle rued the day)
1. (idiomatic) to seriously regret one’s actions
     
30 November 1989, Chicago (IL) Sun-Times, pg. 4:
Unimpeachable sauce will roux the day
By Joan Drake
 
Twitter
Josh Simon‏
@jss1113
Do chefs who burn their butter-and-flour mixtures have to roux the day?
5:04 PM - 19 Apr 2010
 
Twitter
David Leibowitz‏
@davio1962
Thinking about adding flour to your saucepan of hot butter?  Oh, you’ll roux the day, my friend.
11:30 AM - 19 Mar 2011
 
Twitter
John Gibson‏
@SandyFootwells
If you begin making a flour and butter base for sauces you’ll roux the day you started.
10:51 AM - 27 Aug 2011
 
Twitter
Hab§Pøwerbeard‏
@Meadmakesmymorn
My dad always said “You’ll roux the day you mix flour into melted butter.”
11:24 PM - 1 Jun 2012
 
WorldCat record
Roux the day
Author: Peter King
Publisher: New York : Mysterious, 2014.
Series: Gourmet Detective Mysteries.
Edition/Format:   eBook : Document : Fiction : English
Database: WorldCat
Summary:
Murder, madness, and Cajun mayhem follow the detective to New Orleans. For five generations, the Belvedere family restaurant has been a Louisiana landmark. Unfortunately, the Belvedere clan inherits more than a talent for cooking from each other—they also have an unfortunate tendency of becoming insane. When the latest Belvedere patriarch loses his mind, his son attempts to take over the business, only to find that the ancient family cookbook has vanished—and with it the priceless recipe for the world famous Oysters Belvedere. The Crescent City will never be the sam.
   
Twitter
Bentley Kenneth‏
@JohannFux
I roux the day I heated equal quantities of butter and flour.
1:33 PM - 4 Apr 2016
 
Twitter
David Weingart‏
@filkerdave
If you mix butter and flour you’ll roux the day.
9:48 PM - 8 Dec 2016
 
WorldCat record
Roux the day : a dinner club mystery
Author: Linda Wiken
Publisher: New York, New York : Berkley Prime Crime, 2017.
Edition/Format:   Print book : Fiction : English
Database: WorldCat
Summary:
When TV personality Miranda Myers is found dead during a cruise ship casino night, event planner J.J. Tanner is faced with a boatload of suspects, including herself, and turns to her fellow dinner club members to help find clues that could keep her out of hot water. Includes recipes. By the author of Toasting Up Trouble
 
Reddit—Jokes
My wife insisted on mixing the butter and flour together.
submitted June 11, 2017 by PhantomBanker
I told her she would roux the day.