Weeknight Chicken Pot Pie

Name: Weeknight Chicken Pot Pie
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