Philly Steak & Grilled Cheese

This is from sugardishme.com. Josh and I really liked these. Hunter liked them but they were a bit spicy for him.

Ingredients

• For the Steak:
• 1 pound flank steak, still partially frozen (see note)
• 1 tablespoon Worcestershire sauce
• 1 tablespoon oil
• 1 teaspoon coarse ground black pepper
• ½ teaspoon kosher salt
• ½ cup very thinly sliced onion
• ½ cup very thinly sliced bell peppers
• ½ cup button mushrooms, sliced
• For the Cheese Sauce:
• ½ tablespoon unsalted butter
• ½ cup COLD milk
• ½ tablespoon cornstarch
• 4 ounces shredded Horseradish Cheddar (or sharp white)
• For the Sandwiches:
• butter for the skillet
• 8 slices sourdough bread

Instructions

1. Slice the steak very very thinly -- I cut mine into 2-3" strips, as thin as my knife would allow. Toss the sliced steak with the Worcestershire sauce. Set aside.
2. Heat the oil in a large skillet. Add the steak, sprinkle it with the salt and pepper, and cook over medium high heat, turning occasionally to brown on all sides, about 8 minutes.
3. While the steak cooks, slice your vegetables.
4. Place the butter for the cheese sauce in a small saucepan and let it melt over medium low heat. Stir the cold milk and cornstarch together and then pour it into the melted butter. Let it heat up slowly.
5. Remove the steak to a plate and add the onions, peppers, and mushrooms to the skillet it was in. Let them cook over medium high heat until they are tender, stirring occasionally, about 6 minutes.
6. When the milk mixture is warm (it will be frothy - careful not to scorch it), remove it from the heat and stir in the cheese until it's smooth.
7. Once the vegetables are cooked, add them to the steak and toss to combine.
8. Melt a little butter (I just rub the stick in the pan) in the same skillet you used for the steak and vegetables. Add one slice of sourdough bread. Top the bread with the steak and veggie mixture. Spoon the cheese sauce over the steak. Top with the second slice of bread.
9. Turn the sandwich to grill the second side and repeat with the other 3 sandwiches.
10. EAT.