Preheat oven to 400 degrees F
Chop all chicken and vegetables
Season chicken with salt and pepper
Add butter to large skillet on medium heat
Add garlic when butter bubbles
Once garlic is fragrant, add onion, season with salt and pepper, cook for about 3 minutes
Add all chicken, stirring to brown all sides
Add 1/3 cup beer to chicken and onion. Continue cooking for 5 minutes
Add mushrooms, celery and carrots.
Cover with a lid and cook for 2 minutes on medium-high heat
Add next 1/3 beer, season with salt, pepper, thyme and oregano
Add milk and 1 tbsp flour, stirring
Add last 1/3 of beer, stir and cover with lid for 2 minutes
Add 1 tbsp of flour, stirring and season again with salt and pepper
Bring to a boil and then let simmer, covered, for around five minutes as you prepare the puff pastry
Grease a 2.8 litre casserole dish
Prepare your puff pastry per the instructions on the package, rolling it out to fill the bottom and sides of your casserole dish
Roll out the top portion as well
Pour pie filling into pastry-lined casserole dish
Place second pastry on top, pinching top and bottom together where they meet (don't worry about making this look pretty!)
Place into preheated oven for 30 minutes
After 30 minutes, brush eggwash over the top of the pie (I didn't use the whole egg)
Place back into oven for 15 minutes
After 15 minutes, let pie rest for 5 minutes before serving
Enjoy!