Cook the diced potatoes in a small saucepan of boiling water for 7-9 minutes, or until fork-tender; drain and pour into a large bowl.
Heat 1/2 tablespoon of butter in a large skillet over medium-high heat. Add the chicken then season with sea salt and freshly cracked pepper, to taste. Cook, stirring often, for 3-4 minutes or until cooked through. Remove the chicken from the skillet to the large bowl with the potatoes.
Heat the remaining butter in the same skillet. Add the onion, carrot, celery, and thyme leaves then season with sea salt and freshly cracked pepper, to taste. Cook, stirring often, for 3-4 minutes or until softened.
Add the flour and cook, stirring constantly, for 2 minutes. Add the minced garlic and cook, stirring constantly, for 1 minute.
Slowly add the chicken broth and whisk until well combined. Add the milk and whisk until combined then cook, stirring constantly, until thickened, about 2 minutes.
Remove from the heat and pour into the bowl with the chicken & potatoes; mix well. Taste and re-season if needed. Set aside to cool. Once it has cooled, place it into the refrigerator for at least 15 minutes to cool completely. Once completely cooled, and right before you prepare the pies, add the frozen peas and mix until well combined. Side Note: Having the filling be nice and cold will make working with the pie dough much easier!
Preheat the oven to 375 degrees. Line a baking sheet with parchment paper.
Roll out both of the pie crusts on a lightly floured surface. Using a 4-inch biscuit or cookie cutter (a glass jar or anything round will also work). You’ll need to re-roll the dough to use it all up.
Place a spoonful of the cooled & thickened mixture in the center of 12 of the rounds. Top each round with another pie round and press the edges together very firmly. Roll and crimp the edges. Side Note: You can also make crescent-shaped pot pies with just one pie crust round if you prefer.
Brush some well-beaten egg wash on the top of each hand pie then cut a few slits in the top of the crust for venting. Place on the prepared baking sheet.
Bake for 20-25 minutes, turning halfway through baking, until golden brown. Remove from the oven and allow to cool. Enjoy.