Preheat your oven to 375.
Melt the butter in a saute pan over medium heat, add the onion, celery, carrots and dried thyme
Cook for 3-5 minutes
Add the flour, cook for 1 minute
Whisk in the chicken broth, bouillon and half and half
Bring this to a low boil until it starts to thicken
Reduce heat to low and add in the chicken, frozen peas, frozen corn, salt and pepper
Cover and simmer on low for 15 minutes.
Now for the crust
Add the flour, salt, baking powder and chilled butter to a large bowl
Using a pastry cutter or your fingers distribute the butter in the flour until you have tiny lumps throughout and it's mixed well. Add in the ice cold water one tablespoon at a time
You don't want the dough to be super soft, it can still be a bit crumbly because it will warm as you form it
Bring this into a ball form.
Pour the pot pie filling into a casserole dish or individual oven safe soup bowls
Roll the dough out into one big circle if you are doing a large pot pie or cut into small circle for individual sizes
Lay the crust on top
Combine the egg and water, use a pastry brush to wash over the crust
Use a knife to make a few slits on the top of the crust to let air out
Bake in the oven until the crust turns golden brown
Between 30-40 minutes
Remove it and let it cool for about 20 minutes