Direction

1. Preheat oven to 400°F. Unfold puff pastry sheet, and place on a parchment paper–lined baking sheet. Trim pastry to a 6 1/2- x 10 1/2-inch rectangle; reserve scraps for another use. Lightly score a 1/8-inch-deep crosshatch pattern into pastry using a paring knife, spacing rows 1 inch apart; brush evenly with beaten egg yolk. Bake pastry in preheated oven until puffed and golden brown, about 25 minutes, rotating pan on rack after 15 minutes. Let pastry cool on pan until ready to top pot pie. (Do not turn oven off.)
2. Meanwhile, melt butter in a large skillet over medium-high. Add leeks, onion, celery, pepper, and 3/4 teaspoon salt. Cook, stirring often, until vegetables are softened and just starting to brown, about 7 minutes. Add garlic; cook, stirring often, until fragrant, about 1 minute. Sprinkle with flour; cook, stirring constantly, until a film starts to form on bottom of skillet, 1 to 2 minutes. Gradually stir in bone broth. Bring to a simmer over medium. Cook, stirring often, until thickened, about 8 minutes. Stir in chicken, parsley, capers, and remaining 3/4 teaspoon salt. Remove from heat.
3. Spoon chicken filling into a 7- x 11-inch baking dish. Place cooked pastry over filling. Bake at 400°F until filling is hot and bubbling, 5 to 8 minutes. Let pot pie cool 5 minutes before serving.