In a small bowl, combine the shredded chicken and 1/4 cup of the buffalo sauce, tossing well to coat. Brush one side of each bread slice evenly with softened butter. Set 2 bread slices, buttered-side down.

Start assembling: place one slice of provolone cheese on each base slice of bread, followed by a sprinkle of cheddar cheese. Add half the shredded buffalo chicken to each sandwich stack.

Drizzle each sandwich's chicken filling with 1 tablespoon of the remaining buffalo sauce. Top with blue cheese crumbles if using. Place the second slice of provolone cheese over the chicken, then the remaining bread, buttered-side up.

Heat a large, non-stick skillet over medium heat. Place the assembled sandwiches in the skillet, cover with a lid, and grill for 3-4 minutes, or until the bottom layer of bread is golden brown and the cheese is starting to melt.

Flip the sandwiches, re-cover the pan, and cook for another 3-4 minutes, or until the second side of the bread is golden and crispy and the cheese is fully melted and oozy.

Transfer the sandwiches to a cutting board, let them rest for 60 seconds to set the cheese slightly, then slice diagonally and serve immediately with extra buffalo sauce and ranch dressing for dipping.