Interesting! First thing that came to my mind was "Two flat layers of one substance with another flat layer pressed between." This works for food but also for non-food, sandwich transistors for example, or when you get sandwiched between two Finnish dwarves. But of course this use of sandwich came after the original use which was the food item, and "sandwich" nowadays can mean "something resembling the structure of the sandwich food item."

The idea of an "open-faced sandwich" is particularly interesting. It's like sandwiches became so common that the part of definition about two pieces of bread was no longer important - it is a sandwich because it looks like a sandwich. And if it's missing the top piece of bread well then it's a sandwich that's open. Weird. Is that like a one-hand clap? Or a four leaf clover with 3 leaves? Or related to the fact that I'm half-centaur and my girlfriend is half-mermaid?

Reminds me of a nearby mountain called Forbordsfjellet. "Fjell" = mountain, and Forbord is the little village in front of the mountain. So far so good: Forbord's mountain. But "forbord" means "before the foot of the mountain." The village was named for being at the foot of the mountain, and then the mountain was named later after the village. Before-the-foot-of-the-mountain mountain. Weird.

Sorry - don't want to hijack an awesome discussion about sandwiches with Norwegian mountain names, but this feels connected to open-faced sandwiches somehow.