Melt butter in a large skillet or pot on medium heat, add onions, carrots, celery, and garlic. Cook until they start to soften about 3 minutes.
Add flour and whisk until combined and cook another minute. Add chicken broth and whisk until combined.
Add the potatoes and bring to a low boil, reduce heat and simmer for 7-8 minutes to soften potatoes.
Add chicken, corn, peas, rosemary, thyme, salt and pepper, and cream. Simmer for another 5-6 minutes until it becomes thick and bubbly.
Remove from heat and let cool, the sauce will thicken. If you are freezing the pot pies bring the mixture to room temperature before filling the pies and freezing.
Preheat the oven to 425 degrees
Roll out your pie crust and cut the circles out using a biscuit cutter or glass. Re-roll the dough until you get all the circles cut.
Place the bottom crusts into the tins and spoon the mixture to the top. Then top with the second crust.
Then seal the edges with a fork.
Whisk egg white with 1 tablespoon water brush over top of crust.
Make 2-3 slits in the middle of the top to let the steam release.
Place the pies on a baking sheet lined with aluminum foil in case they spill over. Bake for 30-35 minutes or until the crust is golden brown.