This first experiment isn't pretty to look at, but the beauty is inside. I essentially wanted to make a peanut butter cup sandwich with ingredients more "real" than I'd have if I'd just grilled some Reese's.
My ingredients were honey oat bread, chunky peanut butter, spreadable butter, and two Hershey's bars.
I buttered the bread on the outside, spread the peanut butter on one slice, and laid the chocolate bars on the other slice. It's possible I had too much chocolate. (Is it possible to have too much chocolate?) I think I might have had better results if I used one bar broken up and spaced evenly.
After putting it together, I wrapped the sandwich in foil so that I wouldn't have to clean melted chocolate off my panini grill. That might not be an issue with a single bar with the pieces spaced away from the edge of the bread. The sandwich might look more attractive as well with the grill lines.
I grilled the sandwich for three minutes, but five might have been better for more browning on the inside. Surprisingly, the outside edges of the chocolate weren't melted, but I'm not sure that would have been the case if it were a naked sandwich.
The interior was nice and melty and mixed well with the peanut butter. (See top photo.) One more thing that might improve the sandwich is to use dark chocolate instead of milk chocolate.