01 - Set oven temperature to 400°F and allow to fully preheat.
02 - In a large skillet over medium heat, melt butter. Add diced onion, carrots, and celery. Sauté for 5–7 minutes until vegetables soften. Stir in minced garlic and cook for 1 additional minute.
03 - Sprinkle flour over vegetables and stir for 1 minute until evenly coated.
04 - Slowly pour in chicken broth and whole milk, whisking consistently. Cook and stir for 4–5 minutes until the sauce thickens.
05 - Add cubed cooked chicken, frozen peas, thyme, salt, and black pepper. Mix thoroughly. Remove skillet from heat and allow filling to cool slightly.
06 - Transfer prepared filling into a 9-inch pie dish or divide evenly among four oven-safe ramekins.
07 - On a floured surface, roll out pie dough to cover the dish or ramekins. Use a sharp paring knife to carve jack-o'-lantern facial features into the dough.
08 - Drape carved dough over the filling. Press edges to seal securely. Brush the surface with beaten egg for glossy, golden color.
09 - Place dish in oven and bake for 25–30 minutes (18–22 minutes for individual ramekins), until crust is deeply golden and filling bubbles at the edges.
10 - Remove from oven and let cool for 10 minutes to set before serving.