1. Preheat oven to 425 degrees.
2. Place potatoes and carrots in a small saucepan, cover with water, and bring to a boil for 5-8 minutes to soften. Drain
3. Melt ½ cup butter in a large saute pan. Add onions and saute for 2 to 3 minutes.
4. Add salt, pepper, thyme, and poultry seasoning. Sprinkle flour on top and cook for 1 minute, stirring to evenly cook the flour.
5. Gradually whisk in chicken broth and then milk. Add potatoes and carrots and let simmer for a few minutes to thicken. Check for seasoning and add more salt and pepper if desired.
6. Stir in chicken and peas. Turn off heat.
7. Fit 1 pie crust into the bottom of a deep dish pie plate. Pour filling into pie shell.
8. Place second pie crust on top and trim excess. Press the two pie crusts together to seal and crimp edge using your fingers.
9. Brush egg white on top of the pot pie and use a knife to cut 4 slits to let steam escape.
10. Place on a baking sheet and place in oven and back for 30 minutes.