4 skinless, boneless chicken breast halves (1 1/2 pounds)
1 bay leaf
1/3 cup walnuts pieces
1/2 cup mayonnaise
1 tablespoon Dijon mustard
1 tablespoon finely chopped tarragon
1 tablespoon snipped chives
1 tablespoon fresh lemon juice
Freshly ground pepper
4 celery ribs with leaves from the light green inner heart, finely chopped
Preheat the oven to 350°. In a medium saucepan, cover the chicken breasts with water. Add the bay leaf and bring to a simmer. Reduce the heat to low and poach the chicken until white throughout, about 10 minutes. Discard the bay leaf. Transfer the chicken to a work surface and let cool slightly, then cut into 1/2-inch dice.
Meanwhile, in a pie plate, toast the walnuts for about 7 minutes, or until golden brown. Let the walnuts cool, then coarsely chop them.
In a large bowl, whisk the mayonnaise with the mustard, tarragon, chives and lemon juice. Add the chicken, walnuts and celery, season with salt and pepper and toss to coat thoroughly.
The chicken salad can be assembled and refrigerated overnight. Add the toasted walnuts just before serving.