Preheat the oven. Preheat oven to 425°F.
Cook the vegetables. Melt the butter in a large skillet over medium heat. Add the onion, carrots, celery and ½ teaspoon kosher salt. Cook, stirring occasionally, until the vegetables begin to soften, about 6 minutes. Add the frozen pearl onions during the last 2 minutes of cooking.
5 Tbsp unsalted butter, 1 medium yellow onion, ¾ cup peeled and diced carrots, 1 cup diced celery, ½ cup frozen pearl onions, 1 tsp kosher salt
Add the aromatics. Stir in the garlic and ½ teaspoon dried thyme and cook for about 30 seconds, until fragrant.
2 cloves garlic, ½ tsp dried thyme
Add the flour. Sprinkle the flour over the vegetables and stir until the vegetables are evenly coated. Cook for about 1 minute, stirring constantly.
⅓ cup all-purpose flour
Make the gravy. Stir the Better Than Bouillon into the chicken broth until dissolved. Gradually pour the broth into the skillet, stirring as you add it. Stir in the heavy cream, Dijon mustard, Worcestershire sauce, remaining ½ teaspoon kosher salt and pepper. Continue stirring until smooth and the sauce has thickened enough to coat the vegetables. No prolonged simmering is needed; the filling will thicken further as it cools.
1 tsp Better than Bouillon Roasted Chicken Base, 2 cups low-sodium chicken broth, ½ cup heavy cream, 1 tsp Dijon mustard, 1 tsp Worcestershire sauce, ½ tsp freshly ground black pepper
Finish the filling. Fold in the chicken and frozen peas. Remove from the heat. Transfer the filling to a wide bowl or shallow dish and refrigerate for about 15 minutes while you prepare the bottom crust.
2½ cups cooked chicken, ¾ cup frozen peas
Par-bake the bottom crust. Fit one pie crust into a 9-inch pie plate, gently easing it into the plate without stretching the dough. Prick the bottom and sides several times with a fork. Bake directly on the center oven rack for 8–10 minutes, until the crust is set and just beginning to brown. Remove from the oven and let stand for 2–3 minutes.
2 homemade or refrigerated pie crusts
Add the egg wash. While the crust rests, whisk together the egg and 1 tablespoon water. Lightly brush the bottom and sides of the warm par-baked crust with the egg wash. Reserve the remaining egg wash for the top crust.
1 large egg, 1 Tbsp water
Add the parsley and lemon. Stir the fresh parsley and lemon juice into the cooled filling just before assembling the pot pie.
2 Tbsp chopped fresh parsley, 1 tsp fresh lemon juice
Assemble the pot pie. Spoon the cooled filling into the par-baked crust. Place the second pie crust over the filling. Trim, tuck and crimp the edges as desired. Cut 4 slits in the top to allow steam to escape. Brush the top crust lightly with the remaining egg wash and sprinkle with ¼ teaspoon dried thyme and, if desired, flaky or coarse salt.
¼ tsp dried thyme, Flaky or coarse salt
Bake. Reduce the oven temperature to 375°F. Bake for 35–45 minutes, until the crust is golden brown and the filling is bubbling through the vents. If the crust is browning too quickly, loosely tent the pie with foil.
Rest before serving. Let the Chicken Pot Pie rest for 20–25 minutes before slicing and serving.