Smothered Chicken Waffle Sandwich

Name: Smothered Chicken Waffle Sandwich
Ingredients: 3 tablespoons unsalted butter; 1/4 teaspoon Cajun seasoning; 2 scallions, thinly sliced; 3 tablespoons all-purpose flour; 1 cup chicken broth; 1 cup whole milk; 1 rotisserie chicken, skin and bones discarded, meat shredded (about 4 1/2 cups meat); Kosher salt and freshly ground black pepper; Hot sauce, for seasoning; 3 cups all-purpose flour; 2 tablespoons sugar; 2 teaspoons baking powder; 2 teaspoons kosher salt; 2 cups sour cream; 1 stick (8 tablespoons) unsalted butter, melted; 6 large eggs, lightly beaten; Nonstick cooking spray, for the waffle iron