Add the flour and whisk to ensure there are no lumps before adding the chicken stock. Cook for 5-10 minutes while continuously stirring.
Check the consistency by dipping the back of a spoon into the sauce and running your finger along the spoon. You want the sauce to cling to the spoon and not run over the swipe you made.
Continue to cook and stir the sauce over medium heat until you reach the correct consistency. Season with the salt, pepper, and cayenne (if using). Taste the sauce and see if your sauce needs more seasoning.
Add the cream and stir to combine.
Add the shredded chicken, carrots, potatoes, and peas to the sauce. Cook the vegetables in the sauce for 2-3 minutes.
Transfer the filling to a clean bowl and chill in the refrigerator for 1 hour, or until cool.
Preheat the oven to 400˚F (200˚C).
Roll out the puff pastry, using a bit of extra flour to ensure the pastry doesn't stick to your work surface. Use a bowl or plate about an inch (2 cm) larger than the dish you are cooking your pot pie in as a guide to cut out your pastry.
Carefully spoon the chilled filling into oven-proof serving bowls.
Break the egg in a small bowl and add a tablespoon of water or cream. Whisk with a fork.
Brush the egg wash on the edges and rim of your dishes.
If desired, shave truffles over the filling. Lay the pastry rounds over the top, being careful not to stretch the pastry. Seal the edges of the pastry by lightly pushing it onto the rim of your dish to make sure it is secure.
Brush the top and sides with more egg wash.
Place the pot pies on a large baking sheet and bake for 25-35 minutes, until the pastry is a nice golden, dark brown and there are no more grayish raw patches.