So my first attempt was Mac and Cheese waffles.
I had leftover mac and cheese that was a stovetop version. Mine was jalapeno bacon and broccoli mac and cheese - I think it would work better with mac and cheese with no mix ins - my peppers and bacon were small pieces, but the broccoli was larger and made the waffle a little loose in spots.
I took the mac and cheese and spread it into a 9 x 13 pan in a thin layer. Covered it with foil directly on top, and nested another 9 x 13 pan on top and pressed it to get everything to stick together as much as possible. I refrigerated it overnight this way.
To make the waffles, I cut the pressed mac and cheese into about bread sized slices. I put a layer of cheese in between two slices - colby jack for DS and pepperjack for DH. Preheated the waffle iron and put the mac and cheese sandwich in. I slowly pressed and closed it until it would shut all the way and latch - this probably took about 30 seconds to a minute to get the iron fully closed. I cooked it for about 8 minutes on the middle heat setting of the iron. This was long enough to get the cheese inside all melty and make it golden brown on the outside. Then I took it out, topped with a fried egg and sliced green onions.
I ate a few pieces from DS's without the egg. Obviously not something to eat all the time, but it was a good way to use up leftover mac and cheese. I think that for the size I made for DH, I would use two fried eggs in the future for a better ratio.