Divide pepperoni evenly among 4 slices bread; top each with 1/2 cup cheese. Top with remaining 4 slices bread.
Heat griddle or large skillet over medium heat.
Meanwhile, top each of 4 slices bread with 1 slice cheese. Top each with another slice each bread and cheese and remaining slice bread. Butter top and bottom of each sandwich.
On griddle, cook each sandwich until golden brown on both sides and cheese is melted. Cut each sandwich into 2 triangles.