Roast Beef Sandwich with Caramelized Onions and Grainy Mustard, Horseradish Mayo

No roast beef sandwich would be complete without a hit of tasty gravy, also leftover from the roast beef dinner, and I often like to add something green in the form of peppery arugula. No matter how you do it, you really cannot go wrong with a roast beef sandwich! 

Roast Beef Sandwich with Caramelized Onions and Grainy Mustard, Horseradish Mayo

The best part of the roast beef dinner might just be in using the leftovers to make roast beef sandwiches! Tender roast beef with sweet caramelized onions and the bite of a touch of horseradish.

ingredients

• 1 tablespoon olive oil
• 4 cups onion, sliced
• 1/2 cup water
• 4 buns, cut in half and lightly toasted
• 4 slices cheese, cheddar, swiss or provolone
• 1 pound roast beef, warm and thinly sliced
• 1/4 cup gravy
• 2 tablespoons mayonnaise
• 1 tablespoon horseradish
• 1 tablespoon grainy mustard
• 1 handful arugula (optional)

directions

1. Heat the oil in a pan over medium heat.
2. Add the onions and water and cook, covered, until completely tender and caramelized and golden, about 40-50 minutes, adding more water as needed.
3. Mix the mayo, horseradish and mustard.
4. Assemble sandwiches and enjoy!

http://www.closetcooking.com/2011/11/roast-beef-sandwich-with-caramelized.html