Bring 5 cups of water to a boil. Add the chicken breasts (add more water to cover, if needed). Boil the chicken for 30-40 minutes, or until cooked through.
While the chicken cooks, add a tablespoon of butter to a skillet over medium-low heat. When the butter has melted, add the chopped onion. Sauté until the onion is translucent and just beginning to caramelize, about 30 minutes.
Preheat the oven to 350°F. Strain the chicken breasts. Using a stand mixer with a paddle attachment, shred the chicken until no large chunks remain.
Season with salt and pepper. Add the cream cheese, green onions, sautéed onions, and chopped celery. Stir until combined, then pour in the buffalo sauce. Mix until the sauce has been completely incorporated.
Grease a glass baking dish with oil spray or butter. Pour the buffalo dip into the dish.
In a small bowl, melt the remaining butter and mix with the panko. Stir until the panko is wet and crumbly. Evenly spread the panko mixture over the top of the dip.
Bake the buffalo dip in the preheated oven for 10-15 minutes or until the panko is golden brown. Garnish with the remaining green onions and blue cheese, as desired. Serve alongside chopped celery, carrots, pita triangles, and chips. Enjoy!