Rich and salty, the open breakfast sandwich is an elegant play on the classic Monte Cristo, a variation of a French dish called Croque Monsieur that was first served in Parisian bars and cafes in the early 1900s. It's everything you want in your first meal of the day _ a marriage of sweet and salty under a creamy and nutty blanket of cheese.
I used honey mustard instead of Dijon because that's what I had in the fridge. If you can't find Gruyere, Swiss cheese is a fine substitute.
