Preheat and prep. Heat the oven to 400°F (200°C). If using a ceramic or metal pie dish, place it on a sheet pan and warm it in the oven while you make the filling. This helps the crust set quickly.

Cook the aromatics. In a large skillet or Dutch oven over medium heat, add olive oil and 2 tablespoons butter. Sauté onion, celery, and carrots with a pinch of salt for 6–8 minutes, until soft and lightly golden. Add garlic and thyme; cook 30 seconds.

Make the roux. Add remaining 4 tablespoons butter to the pan. Once melted, sprinkle in flour. Stir constantly for 1–2 minutes until smooth and foamy, without browning. This step prevents a raw flour taste.

Build the sauce. Gradually whisk in chicken stock. Add bay leaf if using. Simmer 5–7 minutes, stirring, until the sauce thickens to a gravy-like consistency. Lower the heat and stir in the cream. Season with 1 teaspoon salt and 1/2 teaspoon pepper to start.

Add the chicken and peas. Fold in the cooked chicken and peas. Simmer 2 minutes. Taste and adjust seasoning—add more salt, pepper, or thyme as needed. Remove bay leaf. Let the filling cool 10–15 minutes; slightly cooled filling keeps the crust from getting soggy.

Line the dish (optional). If you prefer a double-crust pie, gently fit one pie crust into the warm dish. Trim excess and chill for 10 minutes. For a single top crust, skip this step and use a casserole dish.

Fill and cover. Spoon the filling into the prepared dish. Top with the second pie crust or a sheet of puff pastry. Trim, fold, and crimp the edges. Cut 4–5 small slits in the top to vent steam.

Brush and bake. Brush the crust with egg wash for shine and color. Place the pie on a sheet pan to catch any drips. Bake 30–40 minutes, until the crust is deep golden and the filling is bubbling at the edges.

Rest before serving. Let the pot pie rest 10–15 minutes. This helps the filling set so slices hold together.