Question: I guess it's technically a Mornay, it has Parmesan and Fontina. I've got about 1 1/2 cups in my fridge. Refrigerated it's solid enough to hold a knife vertically, when it was warm it was just barely pourable and self spreading. It's a darn good sauce, I'd hate to waste it, but after all my adventures lately making an 'ultimate' lasagna, I won't end up using it for pasta. I'd like to put it to use in an entirely different way, preferably with a totally different flavor profile.

Any ideas?

Bonus points if it would make a nice lunch for the day after the extreme lasagna dinner.

Answer: 
Crouque-Monsier or the similar "Hot Brown" sandwich is perfect for my needs. That will use up the sauce in a completely different way. It will also make a great lunch. Thanks SAJ14SAJ for the tip.
You can mix it with a little bit of tomatoes and pour it over spicy burritos the oven heat makes everything golden brown and crusty.