2) Butter the bread slices on 1 side with butter and place them butter side down. Spread 4 slices with peanut butter and top with the banana slices. Spread the remaining slices with jelly and put them, jelly side down, on top of the bananas. Press them together gently.
3) Place each sandwich on the heated panini press and griddle until the bread is toasted, about 5 minutes.
Alternately: 1) Preheat a dry cast iron pan or non stick pan.
2) Place the sandwich in a heavy pan and weight it down with another pan or a clean brick wrapped in foil. Griddle for 5 minutes, turn the sandwich over, re-weight it, and griddle for another 5 minutes. Serve immediately.