Although, I suppose I changed it up a little bit, so maybe it isn't the "absolute best" anymore. But in my professional opinion, it is pretty darn good. The horseradish sauce really makes this sammy. The horseradish plus the roast beef topped with a little bit of spinach makes it quite delicious. I think you could add some sharp cheddar cheese to round out the flavors completely; although, it certainly doesn't need it.
If you have some leftover steak, you could slice it really thin and sub it for the roast beef. You'll just be thanking me (and Rachael) for the sauce!
Oh, and as a tip, chop your fresh chives (hopefully from your little indoor herb garden that is somehow flourishing this year) using kitchen shears. A little bit of time-saver, plus you can cut them right into your bowl and avoid having to scrape them off a wet cutting board. :)
Roast Beef Horseradish Sandwich (adapted from Everyday with Rachael Ray, December 2010)
For Horseradish Sauce (makes enough for 3-4 sandwiches):
1/2 cup low-fat sour cream (or Greek yogurt)
1 tbsp prepared horseradish
2 tbsp unsweetened all-natural applesauce
2 tbsp panko breadcrumbs (or regular breadcrumbs)
2 tbsp finely chopped fresh chives
salt and pepper, to taste
For Assembly (per sandwich):
1 wheat ciabatta roll, cut in half (or other desired crusty bread)
4 slices of thinly sliced deli roast beef
1 tbsp minced onion
1 tbsp chopped parsley
Handful of spinach leaves
Combine all the horseradish sauce ingredients. Keep in fridge until ready to use.
Heat the roll in a toaster oven (or regular oven) at 350 F for about 3-4 minutes until warmed and slightly browned.
Assemble the sandwich by first spreading a liberal amount of the sauce on half of the roll. Arrange the roast beef, onion, parsley and spinach on the roll. Top with the other half of bread.