Preheat the oven to 425 degrees F (220 degrees C).
Melt the butter on a pan on medium heat and add in the frozen veggies and onions. Cook until onions are transluscnet and veggies are fully warmed through.
Add in the shredded chicken, salt, pepper, and garlic powder and mix until combined.
Add in the flour and mix well until it is all incorporated and no pieces of raw flour remain.
Pour in the chicken broth and heavy cream and mix until it is combined. Allow the mixture to bubble and thicken (reduce the heat if needed). Once the mixture thickens, remove it from the heat and let it cool as you prepare the pie crusts. It will continue to thicken as it cools.
Unroll the pie dough and use a small cookie cutter or measuring cup to cut out circles that are 2.5 inches in diameter. Place these circles into the cups of a mini muffin pan pressing in on the sides as needed.
Once the filling cools, scoop out about 1 tablespoon of filling into each pie cup. Make sure to not overfill the mini cups so that the filling doesn't completely ooze out while baking
Combine the scraps of remaining dough from the pie bottoms and reroll it out. Use a small circle (I used my tablespoon-sized measuring spoon) to cut out small circles about 1.25 inches in diameter for the top of the pies. These tops do not need to completely cover the pies, they are just added to help prevent the pie filling from drying out when baked.
*Optional: Whisk together one egg and one tablespoon of water to form an egg wash to brush on top of the pies. This is not necessary but helps the pies to obtain a shiny brown color. You can also brush a little milk on top of the pies for a similar effect.
Bake the pies for 15-20 minutes or until the crust is golden. Allow the pies to cool completely before serving.