Preheat oven to 375.
Heat a dutch oven or heavy bottomed pan to medium high heat. Add butter.
Once butter is melted, add onions, celery, and carrots. Cook for 3 minutes until tender.
Add chicken, salt and pepper. Stir until chicken is white and mostly cooked through.
Once chicken is mostly cooked, add flour, thyme, chili flake, potatoes, peas, and milk. Bring to a simmer and allow sauce to thicken.
Spray individual pie dishes with non-stick spray and press crusts into dishes. Spoon in filling.
Fold over dough and brush with egg wash.
Bake for 35-45 minutes, until crust is golden brown.