Remove puff pastry from freezer and bring to room temperature
Chop the vegetables to small sizes (roughly 1 inch slices)
Shred the chicken
In a large pan or skillet, melt the butter on medium
Add one tablespoon of flour at a time, mixing vigorously with a fork or whisk
Once combined, add another tablespoon and repeat step above until all the flour is added
Slowly add broth and continue to whisk to combine flour with broth
Let sauce cook on low for 10 minutes on low
Taste sauce and add salt and pepper as necessary
Next, add the heavy cream and stir to combine
Continue to cook sauce for another 5 minutes
In another large pan or skillet, heat the oil over medium
Add the carrots, leeks and onions to heated pan and sauté for several minutes until soft
Meanwhile, add the shredded chicken and frozen peas to the white sauce and stir to combine
Roll out the puff pastry to the size of your pan (if necessary), and arrange it in the pan
Combine the white sauce and vegetables together, stirring to mix well
Pour mixture into the pan arranged with puff pastry at the base
Layer the chicken mix with parsley
Roll out another sheet of puff pastry and arrange it overtop of the chicken mix
Beat 1 egg lightly and coat the top of the puff pastry entirely
Bake uncovered in the oven for 45 minutes - 1 hour