Preheat oven to 400°F. Shred cooked chicken and set aside.
In a large skillet, melt butter on medium heat. Add the onions, carrots, and celery, and cook until the onions are translucent, about 10 minutes.
Add the flour and cook, stirring, one minute more. Whisk in-2 1/2 cups of the chicken stock. Whisk in milk. Add in sherry, if using. Decrease heat to low and simmer for 10 minutes, stirring often.
Add the chicken meat, thyme, sherry, peas, parsley, salt, and pepper and stir well. Taste and adjust seasoning if necessary.
Divide the warm filling among six 10-ounce ramekins.
Unroll pie crust dough onto a cutting board. Cut into 6 rounds, slightly larger than the circumference of the ramekins.
Lay a dough round on each pot pie filling. Fold the excess dough under itself and use the tines of a fork to press the dough against the edge of the ramekins. Cut a 1-inch vent into each individual pie.
Use a pastry brush to apply an egg wash to each pie.
Cut out letters from pie crust scraps. Place letters on the pie and apply egg wash on top of the letters too).
Line a baking sheet with foil, place the pies on the baking sheet. Bake at 400°F for 25 minutes, or until the pastry is golden and the filling is bubbling. Let cool for at least 5 minutes before serving. Serves 6.