Heat panini grill, or hot pan or griddle to about medium/medium low heat.
coat grill or pan with a small amount of butter. (This is so the sanwich will not stick to your cooking surface.)
On 1 slice of bread spread about 1-2 tablespoons of the peanut butter on the bread. Next, place about 1-2 tablespoons of the chocolate chips ontop of the peanut butter. Place a plain slice of bread over to create the sandwich and grill for about 1-2 minutes on each side, or until flatened and gooey inside. (tip: if you are using a pan make sure to put a heavy object or use a spatula to compress the sanwich down.)
Repeat this with the other slices of bread. Slice sandwiches and enjoy!