Turn on the broiler. Place the pepper on its side in a dry skillet and slide it under the broiler until the skin blackens on the side facing up, about 3 minutes. With tongs, turn the pepper so that an unblackened side faces up, and repeat until the skin is blackened on all sides. Place the pepper in a small bowl and cover it or paper bag and let it steam for 5 minutes as it cools down.

When the pepper is cool enough to handle, transfer it to a cutting board, reserving any liquid in the bowl. Remove the blackened skin with your fingers and discard. Using a paring knife, cut open the pepper, remove and discard the stem and seeds, and chop the pepper into 1/4-inch dice. You should have a scant 1/2 cup.

​Place the grated cheddar in a medium bowl and add the cream cheese pieces, the diced red pepper and its liquid, and the red pepper flakes. With a rubber spatula or wooden spoon, cream together thoroughly, about 2 minutes. Season to taste with salt and pepper.

Turn the cheese mixture out onto a cutting board and use a spatula to gather it into a rectangular block about 5 inches long and 3 inches wide, and 2 inches high. Wrap the cheese tightly in plastic wrap and refrigerate for 1 hour, or until ready to use.

​For each sandwich, lightly toast the bread. Shingle the cheese on one side of bread, top with another slice of bread. Melt butter in a small cast iron skillet over medium heat. Place the sandwich in the skillet and pan-fry until golden brown. Flip, cover the skillet, and cook for 3 minutes more, or until golden brown.

Serve at once.