The Ultimate Chicken Potpie

1. Preheat the oven to 400°F. Line a baking sheet with foil and place a large oven-safe skillet on it.

2. In a large pot, heat the butter over medium heat. Add the onion, carrot and celery. Cook until tender, 7 to 9 minutes.

3. Stir in the mushrooms and garlic, and continue to cook until all the vegetables are tender and beginning to turn golden, 5 to 6 minutes more.

4. Stir in the herbs, and season the whole mixture with salt and pepper.

5. Add the flour to the pot, and stir to combine. Cook 1 to 2 minutes, or until the flour emits a toasty aroma. Add the broth gradually, mixing constantly to make sure there are no lumps. Bring the mixture to a simmer.

6. Simmer until good flavor develops and the mixture thickens, 10 to 15 minutes. Stir in the chicken and peas, and bring to a simmer.

7. Stir in the heavy cream and bring to a simmer. Simmer 3 to 4 minutes, or until the stew has developed good flavor. Ladle the chicken mixture into the prepared skillet.

8. Press or roll the two sheets of puff pastry together to make one big sheet. Transfer to the top of the skillet and trim away the excess with scissors. The heat of the filling will make the puff pastry soften, so be sure to press the pastry around the edge of the pan to seal it (we used a fork to give it that pretty crimped edge).

9. In a small bowl, whisk the egg with the water to combine. Brush the egg wash over the puff pastry.

10. Use a paring knife to cut a ½-inch-long vent on the top of the potpie. Bake until the puff pastry is golden brown and the filling is bubbling, 15 to 20 minutes. Let cool 5 to 10 minutes before serving.