Beef and Horseradish Sauce Sandwich

This is one of our all time favorite recipes. When I was pregnant with number 2, we ate this a lot. We served it with a bowl of french onion soup to dip the sandwich in. So good! We particularly like the sauce on the sandwich, but we add a lot more horseradish then what the originally recipe calls for.

Serves 4

BEEF

2 -3 lbs flank steak
1 tablespoon unsalted butter , room at temperature
1 teaspoon Dijon mustard
2 teaspoons kosher salt
2 teaspoons fresh coarse ground black pepper

SAUCE

3/4 cup good mayonnaise (Hellmans)
1 1/2 tablespoons Dijon mustard
1 tablespoon whole grain mustard
1/2 teaspoon white prepared horseradish
2 tablespoons sour cream
kosher salt

FOR THE SANDWICH

Hoagie Rolls
arugula or chopped Romaine
kosher salt
fresh ground black pepper

For the Beef:
Place the beef on baking sheet and pat the outside dry with a paper towel. Mix the unsalted butter and mustards together in a small bowl and spread the mixture over the beef with your hands. Sprinkle evenly with the salt and pepper. Grill until you desired steak temperature is done. We like ours medium. Place steak on cutting board and cut across the grain into thin slices.

SAUCE:

Whisk together all ingredients in a small bowl. Serve at room temperature.

TO MAKE THE SANDWICH:.
Slice open hoagie roll, spread the rolls thickly with the Mustard Horseradish Sauce. Top with slices of beef and arugula/romaine and sprinkle with salt and pepper.