Chicken Pot Pie with Fluffy Buttermilk Biscuits

Modified from America's Test Kitchen's New Best Recipes. This is hands down the best chicken pot pie I've ever tasted, and it's quickly become a comfort food. 
Biscuits:
1 cup unbleached all purpose flour
1 cup plain cake flour
2 teaspoons baking powder
1/4 teaspoon baking soda
1 teaspoon sugar
1/2 teaspoon salt
8 tablespoons (1 stick) unsalted butter, cold, cut into 1/4" pieces
3/4 cup cold buttermilk, plus 1 to 2 tablespoons if needed



Filling:
1 1/2 pounds boneless skinless chicken breasts, each cut into three pieces
4 cups low sodium chicken broth
1 1/2 tablespoons vegetable oil
1 medium onion, chopped fine
3 medium carrots, peeled and cut crosswise 1/4" thick
2 small celery ribs, cut crosswise 1/4" thick
4 tablespoons unsalted butter
1/2 cup unbleached all purpose flour
1 1/2 cups milk
1/2 teaspoon dried thyme
3 tablespoons dry sherry
3/4 cup frozen peas, thawed
3 tablespoons fresh parsley, minced
Biscuits:
1. Pulse dry ingredients together in a food processor fitted with a metal blade. Add the butter and pulse until the mixture resembles coarse cornmeal with a few slightly larger lumps. 

2. Transfer the mixture to a medium bowl and add the buttermilk. Stir with a fork until the dough gathers into moist clumps, adding more buttermilk if needed. Transfer the dough to a lightly floured surface and roll out until it is 1/2" thick. Using a 2.5 to 3" pastry cutter, stamp out 8 rounds of dough. Refrigerate dough rounds covered in plastic wrap until needed, up to 2 hours.

Filling:
1. Adjust oven rack to middle position and heat to 400 degrees.

2. Put the chicken broth in a small pot. Add the chicken (make sure it's covered by the liquid), cover and bring to a simmer. Simmer until the chicken is just done, 8 to 10 minutes. Transfer chicken to a large bowl, reserving 2 cups of the broth in a measuring cup. 

3. Heat vegetable oil over medium high heat in a large skillet. Add the onion, carrots and celery and saute until tender, about 5 minutes. Season liberally with salt and pepper. While the vegetables are sauteing, shred the chicken into bite sized pieces with two forks. Transfer the cooked vegetables to the bowl with the chicken; set aside. 

4. In the same pan, heat butter over medium heat until the foaming subsides. Whisk in flour and cook for about 1 minute. Add the reserved chicken broth, the milk, any chicken juices and the thyme. Bring to a simmer and cook, stirring, until the sauce fully thickens, a few minutes. Season with salt and pepper and stir in sherry. Pour sauce into bowl with vegetables and chicken and stir to mix. Add parsley and peas, stir to combine. Adjust the seasonings to taste.

​Assembly and Baking:
5. Pour the mixture into a 9" by 13" baking dish. Top with the biscuits. Bake until the pastry is golden brown and the filling is bubbling, about 30 minutes. 
Notes: 
  • You can make the filling a day ahead and keep it in the fridge overnight; reheat it before topping and baking. 
  • You can also make individual pot pies in ramekins. Cut the dough rounds to just cover the ramekins and freeze, well wrapped in plastic. Portion the filling in plastic Ziploc bags and freeze. To make, slowly thaw the filling (to prevent the roux from breaking) and heat. Pour into ramekin, top with biscuit and bake 20 to 24 minutes at 400 degrees.
  • If you don't have a food processor, make the biscuits as follows:
    • Mix dry ingredients in a bowl with whisk. Chop *frozen* butter into small shards. Mix butter into dry ingredients with whisk. Add buttermilk and mix with a fork until mostly dry, Knead briefly with hands then roll out and punch biscuits. Be careful not to warm the dough too much with your hands.