Spread just enough butter to cover both sides of each slice of bread.
In a large nonstick pan set over medium heat, add the bread slices and cook until they're an even golden brown on the first side, about 2 minutes. Flip 2 of the slices over and top each with 2 slices of the cheese. Place the other 2 slices of bread on top, toasted-side down, forming 2 sandwiches. Continue to cook the sandwiches until the bottoms are golden brown, about 2 minutes. Flip and cook the remaining side for an additional 2 minutes.