Preheat oven to 400 degrees.
Set out frozen puff pastry to thaw slightly.
In a large saucepan, set over medium heat, melt the butter.
Add the flour and cook, whisking constantly for 3-4 minutes. This will create a light colored roux. Do not let flour brown.
Slowly add the chicken stock, whisking until smooth.
Bring to a boil and then add thyme, bay leaf, onion, celery, carrots and mushrooms. Cook until vegetables are almost tender (about 5 minutes).
Add potatoes, chicken, peas, salt and pepper. Cook until potatoes are tender (about 5 - 8 minutes).
Remove from heat and let cool for 5 minutes. Remove bay leaves and discard.
While filling is cooling. Carefully unroll puff pastry on lightly floured counter. Using one of the ramekins, use it to cut out 8 circles. Use the leftover pastry to create decorative touches like leaves, circles, whatever.
Place 8 (10 ounce) ramekins on baking sheet. Fill each ramekin almost to the top.
Top each ramekin with puff pastry circle. Brush the puff pastry tops with egg wash.
Bake in 400 degree oven for approximately 15 minutes. Watch closely until you the puff pastry is golden brown and the filling is bubbling.
Carefully remove tray of pot pies from oven. Let cool 10 minutes before serving.