As you can see, there were a few problems. My bread stuck to the bottom of the top skillet, so it fell apart as I was taking it out. Also, the bottom slice of bread was almost completely burned. So for the next two sandwiches I didn't bother preheating the skillets, and I only left the one on top on for a minute or two to flatten the sandwich, then just flipped it to cook the top. Those came out perfectly. I didn't get a picture because, hey, we were hungry, and who wants a cold grilled cheese sandwich?
Of course, the most important thing is how it tasted. I would say they were just about perfect. The smoky cheese flavors and the Dijon mustard were fantastic together (I couldn't taste the black pepper). I'll definitely be making these sandwiches again.
P.S. I didn't clarify the butter. I just can't bring myself to care that much about butter. Although I suppose if I had maybe the sandwich wouldn't have stuck.