Chicken-and-Leek Pie

Ingredients

• 3 whole chicken legs
• Kosher salt and freshly ground black pepper
• 1 teaspoon extra-virgin olive oil
• 2 tablespoons unsalted butter
• 1 onion
• cut into 1/4-inch dice
• 1 large leek
• white and pale green parts only
• halved lengthwise and cut crosswise into 1/2-inch pieces
• 1 tablespoon grainy mustard
• 1/4 cup all-purpose flour
• 1 cup low-sodium chicken broth
• 3/4 cup plus 1 tablespoon whole milk
• 1/4 cup heavy cream
• 2 tablespoons coarsely chopped tarragon
• One 14-ounce package all-butter puff pastry
• 1 large egg
• lightly beaten
• 1 tablespoon sesame seeds

Instructions

1. Preheat the oven to 400.
2. On a rimmed baking sheet, season the chicken legs with salt and pepper and drizzle with the olive oil.
3. Roast the chicken for about 30 minutes, until browned and cooked through.
4. Let stand until cool enough to handle.
5. Shred the chicken, discarding the skin and bones.
6. Reserve the pan drippings.
7. Reduce the oven temperature to 375.
8. In a large saucepan, melt the butter.
9. Add the onion and leek and cook over moderate heat until tender, about 5 minutes.
10. Stir in the mustard and the flour and cook until pasty, about 1 minute.
11. Whisk in the chicken broth, 3/4 cup of the milk, the heavy cream and the chicken pan drippings and bring to a simmer.
12. Cook over moderate heat, stirring frequently, until thick, about 5 minutes.
13. Stir in the shredded chicken and the tarragon and season with salt and pepper.
14. Let stand until cool, about 30 minutes.
15. Spread the chicken filling in an 8-by-11 1/2-inch baking dish.
16. On a lightly floured work surface, roll out the puff pastry to a 9-by-13-inch rectangle.
17. Lay the pastry over the baking dish and gently tuck in the overhanging pastry.
18. Using a sharp knife, cut 3 slits in the top of the pastry.
19. In a small bowl, beat the egg with the remaining 1 tablespoon of milk.
20. Brush the egg wash over the pastry and sprinkle with the sesame seeds.
21. Set the pie on a rimmed baking sheet and bake for about 1 hour, until the puff pastry is golden brown and the filling is bubbly.
22. Let stand for 30 minutes before serving.