Preheat the oven to 425 degrees and coat a 9- to 10-inch-diameter deep-dish pie pan with cooking spray.
Melt the butter in a large saucepan over medium-low heat. Add the onion, carrots, celery, and thyme and cook, stirring occasionally for 7-8 minutes. Add the mushrooms and sauté until the juices released by the mushrooms have evaporated and all vegetables are tender, about 5 minutes more.
Add the flour and cook, stirring constantly, for 2 minutes. Stir in the water and Kitchen Accomplice Beef Broth Concentrate
or Beef Bone Broth Concentrate
, scraping up the browned bits, and bring the mixture to a simmer. Continue simmering for 5 minutes, stirring occasionally. Add the beef, stirring to combine, and season to taste with salt and pepper. Transfer the filling to the prepared pie pan and set it aside to cool for 5 to 10 minutes.
Place the pie crust on top of the filling and crimp the edges. Cut several vents in the crust to let steam escape. Place the pot pie on a baking sheet and bake for 25-30 minutes, until the crust is golden brown and the filling is bubbling. Let it cool for a few minutes before serving.