Preheat oven to 425 degrees. Line the bottom of a pie plate with one pie crust.

In a large pot, melt butter and add oil. Add in onion, carrots and celery and cook until softened, about 4-5 minutes. Add in the flour and cook for additional minute. Slowly add in chicken broth (I prefer my pot pies on the thicker side, so I start with two cups…if you like a thinner pie, add in more liquid), stirring as you add. Add in potato, chicken, peas and seasonings and adjust chicken broth as needed (it will thicken up once the chicken and potatoes are added). Bring to a simmer and simmer for five minutes.

Allow chicken mixture to cool for about 15 minutes. Add filling to the bottom crust and top with remaining crust. With remaining crust, weave a lattice pattern across the top) alternatively, top with remaining crust and vent with 4-5 holes). Brush with egg wash, if desired, and bake on top of baking sheet at 425 degrees for 30 minutes. Lower oven to 375 and bake for additional 40-45 minutes or until filling is bubbling. (Check midway through baking…of crust is getting too brown, top loosely with aluminum foil.)