Grilled Beef Sandwich With Caramelized Onions and Blue Cheese Ho

This came from teriskitchen.com I haven't made it yet, but I wanted to add it to my shopping list.

• Ready In: 15 mins
• Serves: 2

Ingredients

•  leftover  grilled steak, cut into 1/4-inch slices
• 1⁄4 cup sour cream
• 1⁄2 teaspoon Dijon mustard
• 1⁄2 teaspoon  prepared horseradish (more if desired)
• 1⁄4 teaspoon Worcestershire sauce
•  salt and pepper
• 2  ounces  crumbled blue cheese
• 1  tablespoon olive oil or 1  tablespoon butter
• 1  large onion, peeled and sliced thin
•  mixed salad green (optional)
• 2  large  crusty  rolls

Directions

1. In a small bowl, mix together the sour cream, mustard, horseradish, salt and pepper.
2. Stir in blue cheese. Set aside.
3. Meanwhile, heat a medium skillet over medium high heat.
4. Add the oil, then the onions.
5. Season lightly with salt and pepper.
6. Saute until very tender and golden, stirring often.
7. To make the sandwiches, split the rolls in half.
8. Place beef slices on bottom half.
9. Top with some onions, then some sauce.
10. Top with the other half of the roll.
11. Wrap in paper towels and heat in microwave 45 seconds or until meat is warm.
12. If desired, remove the top roll and garnish with greens and/or additional blue cheese. Serve immediately.
13. Note: If using freshly grilled steak, omit microwave heating and just heat the rolls.