First, combine your shredded chicken with the buffalo sauce in a bowl. Give it a really good mix until every piece is coated. I like to warm this mixture slightly in the microwave (about 30 seconds) so it doesn’t cool down our sandwich later.
Butter one side of each slice of bread – be generous but not gloppy. Make sure you get right to the edges, as this creates that perfect golden crust. Let the butter come to room temperature first.
On your counter, lay out 4 slices of bread butter-side down. Layer each with a slice of cheddar, then a quarter of your warm buffalo chicken mixture.
Sprinkle each sandwich with 2 tablespoons of blue cheese crumbles, a drizzle of ranch (about 1/2 tablespoon per sandwich), and some diced celery.
Top each with a slice of Monterey Jack, then your second piece of bread (butter-side up). Press down gently to compact everything.
Heat a large skillet or griddle over medium-low heat. Don’t rush this with high heat – the key is giving the cheese time to melt while the bread gets golden brown. When a few drops of water sprinkled on the pan sizzle gently, you’re ready to go.
Place your sandwiches in the pan – you might need to work in batches. Cook for about 4-5 minutes on the first side. You’ll know it’s time to flip when the bottom is golden brown and the cheese is starting to melt at the edges.
Carefully flip and cook another 3-4 minutes until the second side is golden brown and all the cheese is completely melted. If you lift a corner, the cheese should stretch.
Let them rest for about a minute before cutting – this helps everything set up so your filling doesn’t slide out. Cut diagonally and serve while hot and melty.