Ingredients: 3 ounces of prosciutto 6 tablespoons unsalted butter 6 tablespoons all-purpose flour 1 cup chicken broth 1 cup whole milk 1 tablespoon Dijon mustard 1 ½ teaspoons kosher salt 1 teaspoon freshly ground black pepper 2 lbs. boneless, skinless chicken breasts, cut into 1-inch pieces 8...