Leftover Corned Beef Reubens

Leftover Corned Beef Reubens are the ultimate after St. Paddy’s Day sandwich. Loaded with slices of leftover corned beef, a tasty reuben sauce, caramelized onions and Swiss cheese all sandwiched between thick slices of marbled rye bread. 

Sick of corned beef hash? Skip it this year in favor of these Leftover Corned Beef Reubens!

I can’t remember exactly when, but something sparked in me a love for reubens about a year ago and I went on a major reuben kick! I was ordering them everywhere, but I was often let down. I decided to start making them myself at home and haven’t looked back. With St. Paddy’s Day approaching I decided it was time to share the BEST reuben sandwich with you! Meet the Leftover Corned Beef Reuben 🙂

leftover corned beef reubens

The Sauce

The secret sauce as I like to call it, is key to a great reuben.

Want to know the secret? There are many…


sweet pickle relish



worcestershire sauce

Ok, maybe that all sounds like too much, too many flavors running around, but believe me you need them all. Combined they make one heck of a delicious sauce!

The Caramelized Onions


This is where my reubens veer from classic and in the best possible way. Adding caramelized onions takes the sandwich to the next level. They add a touch of sweetness that compliments both the sauce and meat so well. You cook them over low-medium heat for 30-35 minutes, so they do take a bit of time, but they are well worth the wait!

leftover corned beef reubens

The Meat


As the name suggests, you’ll use whatever meat you have left from your big corned beef dinner. I recommend this recipe for corned beef if you don’t already have a favorite of your own. Slice all the leftover meat to the same thickness – it should be pretty thin, but thick enough that you are able to flip it. Once the onions are done caramelizing you will use the same pan to quickly fry the meat on both sides. This adds a little flavor as well as heats up the meat for the reuben.

leftover corned beef reubens

The Bread


The bread is very important to the quality of the reuben. In my opinion, marbled rye is the only way to go. I love the combination of the rye and pumpernickel, both are key to the flavor of the sandwich. I know some people have aversions to one or the other, so plain rye, plain pumpernickel or, dare I say, even white bread if you are adamantly opposed will work. No matter what though, make sure your bread is fresh and the slices are thick!


The Cheese


Swiss cheese. There are no substitutes here. A few slices of thick, good quality swiss cheese is a must on these Reubens… I mean if you hate swiss, or can’t eat cheese, I get it. But… I’m not going to suggest anything but swiss 😉

leftover corned beef reubens

The Assembly


These Leftover Corned Beef Reubens are no joke. They can be tricky to assemble, if you are going to make it a triple – decker like this it’s easier to toast the 3 slices of bread separately.

First, butter both sides of 3 slices of marbled rye.

Toast the first slice in a skillet over medium heat. Top with the prepared corned beef.

Toast the second slice and melt the swiss cheese on top, place that slice on top of the meat. Top the second slice with the sauce and caramelized onions.

Toast the third slice, place on top of onions.

Voila! The perfect Leftover Corned Beef Reuben!

leftover corned beef reubens

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Leftover Corned Beef Reubens

  • Author: Sprinkles & Sea Salt
  • Yield: 2 sandwiches 1x


Leftover Corned Beef Reubens are the ultimate after St. Paddy’s Day sandwich. Loaded with slices of leftover corned beef, a tasty reuben sauce, caramelized onions and swiss cheese all sandwiched between thick slices of marbled rye bread. 



Caramelized Onions

2 tbsp unsalted butter

1 large onion, sliced thin

1 tsp salt


1/2 cup sauerkraut (drained)

2 tbsp sweet pickle relish

1 tbsp ketchup

2 tbsp mayonaise

1 tsp Worcestershire sauce

pinch of salt


2 tbsp unsalted butter

1 pound leftover corned beef

4 slices swiss cheese

6 slices marbled rye bread

caramelized onions



Caramelized Onions 

Melt the butter in a large skillet over medium heat

Add onions, sauté 2-3 minutes

Add salt, stir

Reduce heat to medium-low, continue to sauté for 30-35 more minutes, working with a wooden spoon, toss the onions every few minutes so they do not burn

Once onions are browned to your liking and sweet to taste, transfer them to a bowl and set aside

Do not clean the skillet, you will use it again


In a small bowl combine all sauce ingredients, mix well, set aside


Butter both sides of the 6 slices of bread

Put the same skillet that you cooked the onions in onto the stovetop over medium heat

Add the slices of corned beef, heat/brown on both sides for about 2 minutes*, set aside

Add 4 slices of bread to the skillet, toast on both sides, 1-2 minutes per side, set aside

Add the remaining 2 slices, toast on 1 side ,flip and add 2 slices of cheese to each toasted slice, allow cheese to melt (be careful not to burn the bread)

Take 1 slice of the toasted bread top with half of the corned beef slices, top with the slice of bread with the melted cheese, top with a generous helping of the sauce and caramelized onions, finish with the 3rd slice of toasted bread, repeat for the other sandwich


*you just want to heat the corned beef, you don’t want to cook out all of the grease or it will be too dry

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Leftover Corned Beef Reubens

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