Add the chicken and peas and toss to combine. Remove from heat and add parsley. Set aside.
In a medium saucepan, melt butter over low heat. When butter stops foaming, whisk in flour and cook for three minutes, whisking constantly, over low heat to get rid of raw flour taste.
Gradually whisk in the stock, and cook over low heat until slightly thickened. (This is the veloute.)
Preheat oven to 400.
Place filling in a 3 quart baking dish and pour veloute over the top. Toss gently to combine.
Place puff pastry over the filling leaving gaps on the ends, and cut three slashes across the top to vent.
Beat the egg with 1 TB water. Brush egg wash over the puff pastry.
Bake for 30 minutes until pastry is puffed and golden.
Serve hot.
Recipe by West of the Loop at https://www.westoftheloop.com/2015/02/16/chicken-pot-pie-puff-pastry-crust/