Roast the Chicken& Vegetables: Preheat oven to 375º.
02Rub chicken with 1 T olive oil& sprinkle generously, inside& out, with salt& pepper.
03Toss potatoes, carrots, onions, garlic, mushrooms,& herbs with remaining 2 T olive oil& some salt& pepper.
04Set the chicken breast-side down in a large flameproof roasting pan& scatter the vegetables around the chicken.
05Roast for 1 1/4 hours, stirring vegetables several times.
06Remove chicken form the pan to cool.
07Remove vegetables with a slotted spoon& set aside in a bowl with the peas.
08Don't clean out the roasting pan.
09When the chicken has cooled (at least 15 minutes) pull the meat form the bones, discarding skin& bones.
10Cut meat into small chunks (1/2" to 1") & set aside (do this after the sauce is made or while someone else is making the sauce).
11Make the Sauce: If there are not a lot of juices & fat in the pan, skip to step 15.
12If there are, pour the fat & juices into a measuring cup or gravy separator; separate the fat from the juice.
13Add juices to the chicken stock& add enough butter to the fat to make 6 T total fat & butter.
14Put the roasting pan (which should still have caramelized bits in it from the chicken& vegetables) on the stove over medium heat.
15Pour in the 6 T fat+butter; when melted & bubbling, add flour & stir constantly to make a smooth roux.
16Scrape up any caramelized bits.
17Cook the roux, stirring constantly, until lightly browned, about 5 minutes.
18Add the stock, bring to a boil,& simmer.
19Continue to stir & scrape the bottom of the pan.
20Cook the sauce for at least 15 minutes, whisking occasionally, until it is as thick as heavy cream.
21Season with salt, pepper,& more herbs to taste.
22Make the Egg Wash: Whisk together the egg yolk& cream.
23Set aside.
24Assemble the Pot Pie (s): Preheat oven to 400º.
25Choose 4 ovenproof bowls (18 oz each) OR a 2-qt casserole.
26Cut out a circle template of foil or paper that is about the size of the rim of each bowl or casserole.
27Divide the chicken, vegetables,& sauce among the dishes.
28Place on a baking sheet (to catch any drips in the oven).
29For individual pies: On a floured board, cut the dough into 4 pieces.
30Quickly roll out each piece into a larger circle than the circle template (the extra dough will drape down the sides of the bowls).
31Remember to work quickly so the butter in the pastry doesn't start to melt- you may need to sprinkle dough to keep the pastry from sticking.
32As each one is rolled out, place on top of the filled bowls, pressing along the edges.
33For one large pie, lay the dough on a floured board& roll out to a the same shape, but larger than, the casserole template (the extra dough will drape down the side).
34Remember to work fast so the butter in the pastry doesn't start to melt- you may need to sprinkle dough to keep the pastry from sticking.
35Lay the dough on top of the filled casserole& press along the edges.
36Brush the Egg Wash onto the pastry with a pastry brush.
37You do not need to make any vent holes- steam will escape along the edges of the pastry.
38Bake for 30 to 55 minutes, until the crust is thoroughly browned& puffed.
39NOTES: Advance Preparation: The Puff Pastry and the filling (chicken, vegetables,& sauce mixed together) can be made 1 to 2 days ahead of time& refrigerated.