Preheat Oven : Preheat oven to 400°F (200°C). Grease a 9×9-inch baking dish or individual ramekins.
Cook Vegetables : In a large skillet, melt butter over medium heat. Add onions, garlic, carrots, and potatoes. Cook for 5–7 minutes until slightly tender.
Make Creamy Base : Sprinkle flour over vegetables and stir for 1–2 minutes. Gradually pour in chicken broth and milk, stirring constantly until mixture thickens.
Add Chicken u0026 Seasoning : Stir in cooked chicken, peas, thyme, salt, and pepper. Cook 2–3 minutes until filling is hot and creamy. Remove from heat.
Prepare Crust : Roll out puff pastry sheet to fit over the baking dish. Place over filling.
Create Pastry Bones : Roll out extra dough and cut into bone shapes. Place on top of the pie for a spooky effect. Brush entire crust, including bones, with beaten egg for golden color.
Bake : Bake for 25–30 minutes, or until pastry is golden brown and filling is bubbling.
Serve : Let the pie cool slightly before serving to allow filling to set.