Roast Beef and Cheddar Panwiches with Caramelized Onions and Horseradish Mayo

Panwiches.  

Cheesy, gooey, roast beef and cheddar toasted sandwiches with sweet caramelized onions and a zippy horseradish mayo, made in a pan all at one time.  Think of all the precious time you will save by not having to stand there and grill each one.

I know, right?

How fun is that?

These were knockout awesome delicious and now my wheels are turning for more panwich variations. 

Here are my notes:

--This would be terrific with a big pot of soup.  Although I didn't, I feel certain you could assemble this earlier in the day and then refrigerate until you're ready to cook it or maybe even the day before.

--I know you're sitting there saying "but the meat and cheese are covering everything!"  No biggie.  You just slice throughout that in the end.  And let me tell you, you are going to want that cheese to leak out a little bit because when it gets golden and a little crispy around the edges?  SHUT UP!

--My bread was sort of oblong and it overlapped.  This was no problem, though, and in the end, I just cut each row into thirds because this sandwich is kind of rich.  You can use a pan that will fit your bread size if you have it.  Or just overlap it.

--I like my onions golden brown but not all the way super caramelized.  But if you like them SUPER caramelized and much browner, increase your cooking time.  

--My casserole dish measured measured a weird 11 x 12 1/2 inches.  Just substitute with a similar size baking dish, like a 9 x 13.

Roast Beef and Cheddar Panwiches with Caramelized Onions and Horseradish Mayo

Printable Recipe

2 tablespoons extra virgin olive oil

2 tablespoons butter

3 medium onions, thinly sliced

2 teaspoons worcestershire sauce

1/2 cup mayonnaise

3 tablespoons horseradish

3/4 cup melted butter

1 teaspoon dried mustard

1 tablespoon Worcestershire sauce

12 slices sour dough bread

3/4 pound deli sliced roast beef

1/2 pound (approx.) sliced cheddar cheese (I used 17 slices)

1. Preheat oven to 350 degrees.
2. In a large skillet, add olive oil and 2 tablespoons butter over medium high heat.  When butter is melted, add onions and cook until golden brown and caramelized, about 15 minutes, stirring often.  Stir in 2 teaspoons Worcestershire sauce.  Remove from heat.
3. Stir together the mayonnaise and horseradish.  Set aside.  
4. Melt 3/4 cup butter in a small saucepan; whisk in the dried mustard and 1 tablespoon Worcestershire sauce.  Brush the bottom and sides of a 9 x 13 inch metal pan or glass casserole dish generously with about a 1/3 of the butter mixture.  
5. Spread one side of each slice of bread with the mayonnaise.  Place 6 slices of bread, mayo side up, in the bottom of the pan evenly.  
6. Place the beef evenly on the bread, followed by the cheese. (It’s okay to overlap them and cover all the bread.)  Spread the caramelized onions on top of the cheese.  Place the remaining 6 slices of bread mayo side down on the onions, lining up with the other bread.  
7. Generously brush the top of the bread with the remaining butter mixture.  Bake for 20 minutes, or until cheese is melted and the top is golden brown, placing under broiler if necessary to brown the top.  Let cool for 10 minutes before cutting apart into individual sandwiches.