Place the bread slices on a work surface and spread the peanut butter on 1 slice of bread and the jam on the other; set aside.
Melt the butter in a large frying pan over medium heat until foaming. Add the 2 slices of bread filling-side up and cook until the bottoms are golden brown and the filling is warmed through, about 6 minutes.
Using a flat spatula, flip 1 slice of bread onto the other to close the sandwich. Transfer to a plate and serve immediately.