My mom used to make these all the time for an afterschool snack, but she got it from a 1930's church cookbook.
The basic recipe makes a nice simple sweet when eaten alone, but the possibilities are endless. I've mixed in chocolate chips, or dried fruit to make more of a granola bar. It is also nice served warm with ice cream.
I like to make these on cooler days to serve with french onion soup. Using lite mayo instead of butter on the outside of the bread gives me more even browning and fewer calories. You can also make several on a cookie sheet and broil for a few minutes on each side.