There is actually a utensil that makes these. The utensil has long handles with wooden ends on it. The other ends are square or round cast iron disks. It kind of looks like a large pair of tongs, but the business end is at the other end from where it would be on tongs.
The two disks are concave to hold a filled "pie". You butter the outside of the bread or rolls and put filling on one slice. You don't have to cut the bread to the correct shape or size. Put one slice on one disk, put the filling on it, and cover with the second slice. Make sure the buttered sides face the disks. When you close the piemaker it will automatically cut off the unused part and seal the pie.
The you hold it over your fire, checking occasionally to see if it is done.
When I was a kid we would make these on the gas stove in the kitchen and take them wrapped in newspaper to the Red Sox games in Boston!
My favorite was fresh blueberries with sugar and butter!