01 -
Combine flour, sugar, and salt in a large bowl. Add cubed butter and toss to coat. Roll the butter into thin sheets with a rolling pin on a clean surface, combining it with the flour. Use a bench scraper as needed to gather the mixture back into a pile. Chill mixture in the freezer for 15 minutes.
02 -
Remove mixture from freezer and add buttermilk. Stir with a spoon and then your hands until dough forms a ball. Add cold water as needed. Divide dough into two disks, wrap in plastic wrap, and chill in fridge while preparing the filling.
03 -
Heat butter in a large skillet over medium-high heat. Add onion, carrots, celery, and garlic. Cook until tender, stirring occasionally. Stir in flour, salt, black pepper, thyme, parsley, chicken broth, and heavy cream. Simmer over medium-low heat for 10 minutes or until sauce thickens. Add chicken and peas, and set aside.
04 -
Preheat the oven to 400°F.
05 -
Roll out one dough disk on a lightly floured surface into a 12-inch circle, about 1/4 inch thick. Place it into a 9-inch pie pan. Trim excess dough and add the filling.
06 -
Roll out the second dough disk and place it over the filled pie. Trim excess, seal edges by crimping, and cut small slits in the top. Brush crust with beaten egg.
07 -
Bake for 45 minutes or until crust is golden brown. Use a pie crust shield to protect edges if they brown too quickly. Cool for 10 minutes before serving.