I found this recipe on a website called Choice Cooking Recipes. I have never found a prepared dijon-mayo blend, so I just use 1/2 tablespoon dijon mustard and 1/2 tablespoon mayonnaise, and blend the two conditments together with a knife. Most in my family like this sandwich with a few thin slices of red onion added, but that's our own addition (it's not a part of the original recipe), so I've listed that as an optional ingredient.
- Preheat the oven broiler. Line a baking sheet with aluminum foil.
- Open the sandwich roll onto the prepared baking sheet. Spread the mustard-mayonnaise blend on one half of the roll. [NOTE: use 1/2 tablespoon Dijon mustard and 1/2 tablespoon mayonnaise if you don't have a prepared dijon-mayo blend on hand]. Top with turkey, Swiss cheese, and ham (in that order) on top of the mustard-mayo mixture.
- Spread 1 tablespoon of mayonnaise on the other half of the roll. Top with the roast beef, tomato slices, onion slices (if using), and Muenster cheese.
- Broil the sandwich open-faced until the cheese melts and begins to bubble and the ham begins to crisp around the edges.
- Remove the sandwich from the oven and put both sides together. Serve while sandwich is still warm.