Instructions

1. Remove puff pastry from the freezer to let thaw at room temperature then careful unfold. 
2. Preheat oven to 400 degrees.
3. Add butter to a large cast iron or oven safe skillet over medium high heat.  Add carrots, celery, onion, garlic, and thyme; sauté for 7-9 minutes or until veggies are starting to get tender.
4. Stir in flour until no clumps remain and a thick paste forms, then gradually whisk in milk, broth, garlic powder, salt, and pepper, and simmer until mixture starts to thicken.  
5. Add in chicken and peas and continue simmering while you prepare the puff pastry.  
6. For the puff pastry, you can either do a lattice top like I did, or to keep it extra simple can simply roll out and place the whole piece on top, making sure to cut a few slits for the steam to release.  If you choose to do the lattice top, roll out the puff pastry and then cut into 12 even strips.  Start by arranging 6 of the strips going the same direction across the top evenly spaced.  Then fold back the 1st, 3rd, and 6th strips, and place a strip underneath going perpendicular.  Carefully unfold 1st, 3rd, and 6th strips over the new strip you just put down.  Repeat with 2nd and 4th strips and so on and so forth until all strips have been laid out. 
7. Now, whisk egg and 1 T water together in a small bowl.  Brush the egg wash all over the tops of the puff pastry.  Bake uncovered for 30-35 minutes until top is a deep golden brown and mixture is bubbling.  If the top seems to be browning too quickly, you can always cover with foil for remaining time.  
8. Let cool for a few minutes before serving, and enjoy!!