In a bowl, mix shredded chicken with buffalo sauce and cream cheese until well combined. Stir in ranch or blue cheese dressing if using.
Butter one side of each bread slice. Place two slices butter-side down on a flat surface.
On the unbuttered side, layer half the cheddar cheese, then the buffalo chicken mixture, then the remaining cheddar cheese. Top with the second slice of bread, buttered side up.
Heat a nonstick skillet or griddle over medium heat. Cook sandwiches 3–4 minutes per side, pressing gently, until golden brown and the cheese is melted.
Remove from skillet, let rest 1 minute, then slice and serve warm.