Method

To roast the chicken:

1. Preheat the oven to 400°F.

2. Sprinkle the chicken legs with salt and pepper and drizzle with olive oil.

3. Place the chicken legs on a large heavy rimmed baking sheet and roast for 20 minutes.

4. Turn the chicken legs over and continue roasting for 20 minutes, or until the chicken legs are golden brown and cooked through. Set aside to cool slightly.

5. Reserve the pan drippings on the baking sheet.

6. Shred the chicken meat into large chunks and place the chicken in a bowl.

7. You should have about 12 ounces of chicken meat. Discard the sinew, bones and skin.

To prepare the filling:

1.  

   Melt the butter in a large heavy saucepan over medium heat.

2. Add the onion and leek and sauté for 5 minutes, or just until tender.

3. Stir in the mustard then the flour and cook over low heat for 2 minutes, stirring constantly.

4. Slowly whisk in the chicken broth, 3/4 cup of milk, the cream, and the reserved pan drippings.

5. Simmer for 5 minutes, stirring occasionally, or until the sauce thickens.

6. Stir in the shredded chicken and tarragon and season to taste with salt and pepper.

7. Chill until cool.

To assemble pie:

1. Preheat the oven to 375°F.

2. Spoon the chicken mixture into a 1 1/2-quart baking dish.

3. Roll out the sheet of puff pastry into an 11-inch-square.

4. Drape the puff pastry over the pie and press it against the rim of the dish to seal.

5. Cut slits into the pastry to allow steam to escape.

6. Mix the egg and remaining 1 tablespoon of milk in a small bowl to blend.

7. Brush some of the egg mixture over the pie and garnish with sesame seeds.

8. Set the pie on a heavy baking sheet and bake for 50 minutes, or until pastry is golden brown.

9. Set aside for 30 minutes to cool slightly.