Place the chicken breasts in the bottom of the crock pot.
Add diced carrots, celery, onion, and minced garlic on top of the chicken.
Pour in the chicken broth and sprinkle dried thyme, dried parsley, salt, and black pepper over the ingredients.
Cover and cook on low for 6 hours, or until the chicken is cooked through and vegetables are tender.
Remove the chicken breasts from the crock pot and shred them using two forks.
In a medium saucepan, melt the butter over medium heat.
Whisk in the flour and cook for 1-2 minutes until lightly golden to form a roux.
Gradually whisk in the milk and heavy cream, stirring constantly until the mixture thickens and becomes smooth, about 3-5 minutes.
Add the shredded chicken, frozen peas, and frozen corn to the crock pot.
Pour the cream sauce into the crock pot and stir to combine everything evenly.
Cover and cook on low for an additional 15 minutes to heat through and allow flavors to meld.
Preheat the oven to 400°F (200°C).
Place the pie crust squares on a baking sheet lined with parchment paper and bake for 8-10 minutes or until golden and crisp to make pot pie croutons.
Serve the soup hot, topped with the baked pie crust squares.