Heat 2 tablespoons butter tablespoons in a large pot. Add sliced garlic and saute for a minute till flavour gets released, and then add the diced onions and green chilies.
Saute till the onions are translucent, and then add mushrooms.Cook the mushrooms for 2 minutes, and then add chicken.
Cook the chicken till it changes colour from pink to white, and add sliced capsicum.
Cook for a minute and add the mixed frozen vegetables.
Saute for a minute and then add the remaining 2 tablespoons butter.
Add flour and cook for about 1 – 2 minutes till the raw flavour disappears. Make sure to mix well with a spatula, so the flour doesn’t clump.
Add the milk and chicken stock, and bring to a boil while stirring constantly. It’s best not to add all the milk and chicken stock at once. Reserve about ½ cup to adjust consistency.
As the sauce comes to a boil, it will start to thicken. Add salt, Italian herbs, soy sauce, sriracha sauce, black pepper, white pepper and red chili powder or flakes. Taste and adjust seasonings if required.
Pour the chicken pot pie filling into one large baking dish or two smaller dishes. This amount of filling was enough for one large baking dish (36 cm x 22 cm) and one small baking dish (22 cm x 13.5 cm).
Roll out puff pastry if using a block of puff pastry, otherwise thaw a puff pastry sheet for a few minutes.
Cover the baking dish with puff pastry. Cut slits with in the middle and edges. Decorate with leftover pastry scraps and/or crimp the edges with a fork.
Make an egg wash by beating an egg with a fork in a small bowl. Use a pastry brush to spread the egg wash on the puff pastry.
Bake in the oven till puff pastry is golden brown and the chicken pot pie is bubbling hot. This can take anywhere from 15 – 30 minutes, depending on the size of the baking dish used as well as the puff pastry brand.