Chicken

1. In a large stockpot add the chicken breasts and cover with water add salt pepper and bay leaves. Place over medium heat and cook for 15-25 minutes or until the chicken reaches an internal temperature of 165°F/ 74°C. 
2. Transfer chicken to a bowl to cool for 10 minutes. Keep the liquid the chicken cooked in to use as the chicken broth for the pie filling. I like to chop half of the chicken into chunks and take the other chicken and shred it by using a hand mixer to quickly and easily shred it. Set the chicken aside. 

Pie

1. Preheat the oven to 425°F/218°C. 
2. In a large 12" oven-safe skillet or dish add the butter and melt over medium-low heat. Add the onion and saute for a couple of minutes then add the celery and carrots and a pinch of salt and pepper then saute for five-ish more minutes, the onions will be translucent and the celery and carrots will have started to ever so slightly soften. 
3. Add the garlic, flour, and remaining salt and pepper. Stir well and cook for a couple of minutes until all the flour has transformed into a thick paste-like consistency.
4. Now deglaze the pan by slowly adding the chicken stock and using a wooden spoon to scrape the bottom of the pan, all those brown bits are super flavorful. Once all of the broth is added slowly stream in the milk. Now mix continuously for a few minutes, until the mixture has thickened. Add in the chicken and combine, then finally the frozen peas. Remove from heat and set aside while you prepare the top. 
5. On a clean work surface roll out the puff pastry sheet and roll into a 14"X8" rectangle, reroll back onto the rolling pin to gently move on top of the skillet, and unroll there. One side will be slightly exposed, use a sharp knife to cut the excess and use the excess to cover up the exposed pie filling. Take another sheet of puff pastry and roll out slightly then cut squares to use as decoration around the side of the pie. Use a designed cookie cutter if desired.
6. Use an egg wash to brush the back of each decoration so that it sticks to the pie top. Cover the whole pie with an egg wash and cut a slit or two in the center to let steam escape and bake for 20 minutes, if the pastry is browning too quickly cover with foil and bake for an additional 5-10 minutes, you want deep golden brown pastry and a bubbling pie filling. Let cool for at least 5-10 minutes before serving.