In a small bowl, stir the Nutella and cheese together.

To assemble: Butter one side of each slice of bread. Place 4 slices on your work surface, buttered side down. Spread the cheese mixture evenly over the 4 slices so that it is about ¼ inch thick (if it's any thicker, the sandwich will be too gooey). Place the remaining 4 bread slices on top, buttered side up. Cut off the crusts (this helps pinch the bread together to create a tight seal).

Stovetop method: Heat a large nonstick skillet over medium heat for 2 minutes. Put the sandwiches in the skillet (in batches if necessary), cover, and cook for 2 minutes or until the undersides are golden brown and the cheese has begun to soften. Uncover, and turn the sandwiches with a spatula. Cook for 1 minute or until the undersides are golden brown. Turn the sandwiches again, and cook for 30 seconds, or until the cheese is soft and creamy. Serve immediately.

Sandwich maker method: Because of the creaminess of the filling, a sandwich maker does not work for this sandwich.

Gas grill method: Brush a grill rack with oil and preheat the grill to medium. Follow directions for sandwich assembly. Put the sandwiches on the grill and follow directions for the stovetop method.