We Were Very Excited for a Split Second
This person must be very good at geometry… And cooking. They were able to make three perfect grilled cheese sandwiches all in the same shape and size and packed them neatly in a rectangular box. When one of the diagonal sandwiches was removed, it looked like someone had cut a piece of cake out of a pyrex pan.
That would make this a grilled cheese cake! You may be disappointed now, but at least you’ve been given a neat idea of something you can make yourself. You’ll probably have to bake your own bread to make a slice big enough for the pan. Good luck finding a panini press big enough to get the cool grill marks.