Ingredients

• 1 (14- x 10-inch) sheet frozen puff pastry (such as Dufour), thawed

• 1 large egg yolk, beaten

• 8 tablespoons (1 stick) unsalted butter

• 3 leeks, trimmed and thinly sliced (about 2 cups)

• 1 yellow onion, chopped (about 1 1/2 cups)

• 2 celery stalks, chopped (about 1/2 cup)

• 1/2 teaspoon black pepper

• 1 1/2 teaspoons kosher salt, divided

• 4 garlic cloves, finely chopped

• 1/3 cup all-purpose flour

• 2 1/2 cups chicken bone broth

• 4 cups shredded rotisserie chicken (about 1 pound) (from 1 chicken)

• 1/2 cup chopped fresh flat-leaf parsley

• 1/4 cup drained jarred capers in brine