Waldorf Chicken Salad Bagel Sandwich

1/2 cup mayonnaise

2 tablespoons buttermilk

1/2 teaspoon salt

1/4 teaspoon ground black pepper

12 ounces cooked skinless chicken breast halves, cut into 1/2-inch cubes

1 cup seedless red grapes, halved

1 gala apple, cored and cut into 1/2-inch cubes

1 rib celery, chopped

2/3 cup walnut halves, coarsely choppped

2 tablespoons chopped chives

1 tablespoon chopped tarragon

4 sesame bagels, halved horizontally

1. To cook the chicken, bring 3 cups chicken broth to a simmer in a large skillet over medium heat. Add 3 boneless skinless chicken breast halves, 1 pound, and cook, turning once or twice, until a thermometer inserted into the thickest portion registers 165F, about 12-14 minutes. Transfer chicken to a plate and allow to cool before cutting.
2. Combine the mayonnaise, buttermilk, salt and pepper in a bowl. Combine the chicken, grapes, apple, celery, walnuts, chives and tarragon in a separate bowl. Add mayonnaise mixture to the chicken mixture and stir well to combine.
3. Toast the bagels. Place 4 bagel bottoms onto each of 4 plates and top each with 1/4 of the chicken mixture. Set bagel tops onto salad and serve.