Roast Beef Pull-Apart Sandwiches with Homemade Horseradish Sauce

Horseradish Sauce:

1. In a small bowl, whisk together the sour cream, prepared horseradish, Dijon mustard, mayonnaise, salt, and pepper.
2. Taste and adjust the seasoning or horseradish to your preference for heat.
3. Let the sauce sit for at least 30 minutes in the refrigerator to allow the flavors to meld.

Roast Beef Pull-Apart Sandwiches:

1. Preheat the oven to 350 degrees Fahrenheit.
2. To assemble the sandwiches, slice the package of rolls in half horizontally, keeping the individual rolls intact.
3. Remove the top half of the rolls and set aside.
4. Spread the prepared horseradish sauce first on the bottom rolls, then layer with roast beef, caramelized onions, and cheese slices.
5. Place the top rolls back onto the layered sandwich.
6. Brush the top with melted butter (optional).
7. Bake at 350 degrees Fahrenheit for about 8-10 minutes or until the rolls are golden brown and the cheese is melted. Enjoy with French onion soup or by itself.