Make the Pie Crust:

1. Add the flour into a large bowl. Add in the diced butter and toss to coat with the flour. Work the butter in the flour using a pastry blender. Or, using your fingers by squeezing the butter chunks until they're flat and then rub the butter into the flour. Some larger pieces can remain, up to the size of a marble. Continue this until the dough looks shaggy.
2. Make a well in the center of the flour mixture, and add in the sour cream. Using a spatula combine the sour cream in the flour.
3. Using your hands, knead the dough a few times to help blend the sour cream into the flour, until it just comes together as one large ball. Transfer the pastry to a work surface and divide it into two pieces, each about 12 ounces. Shape into a rough disk shape.
4. Place each in a piece of plastic wrap and wrap tightly. Using a rolling pin, roll the wrapped dough out until it stretches to the corner of the plastic wrap. Refrigerate for at least 2 hours, but preferably overnight.

Make the Filling:

1. Heat oil over medium in a dutch oven. Once hot, add onion, celery and carrot and cook for 5-7 minutes, or until they are beginning to soften. Add in garlic, salt, pepper and thyme and cook for 30 seconds.
2. Add in the butter and flour and cook, stirring, until butter is melted.
3. Slowly, stir in half a cup of stock at a time, scraping up the bottom, and stirring as you go, to ensure no lumps. Once all the liquid is added, add in the chicken.
4. Bring the mixture up to a boil, then reduce the heat to simmer for about 15-20 minutes, or until the sauce is thickened and the veggies are cooked through.
5. Shut off the heat, and stir in the peas, lemon, and fresh thyme. Taste and adjust seasoning, adding in more salt, pepper and lemon as needed.
6. Transfer the filling to a shallow container and let cool completely at room temperature, or overnight in the refrigerator.

Assemble and Bake:

1. When ready to bake, preheat the oven to 400ºF.
2. Roll out one pie dough to a 12″ circle. Fit pastry in a 9” pie plate, making sure to press the pastry into the sides and the bottom.
3. Transfer the cooled chicken pot pie filling inside of the pie crust.
4. Roll out the top crust to a 10″ circle and place it on top of the filling. Seal the edges of the pie dough together and crimp as desired. Pierce a few steam holes in the center of the pie, and brush the top with an egg wash.
5. Bake in the preheated oven on the lower rack for 45-50 minutes, until the crust is light golden brown and the filling is completely heated through (reaching a temperature above 170ºF).