Melt 1 T butter in heavy saucepan.
Add and cook onions, carrots and celery over medium heat.
Add thyme, rosemary and bay leaf.
Cook until vegetables are tender.
Add chicken, cook a few minutes until chicken turns white.
Add stock, bring to a simmer and continue to cook a few more minutes while you make roux.
To make roux, melt remaining 4 T butter in a small saucepan.
Stir in flour until well blended.
Cook over low heat, stirring often.
Remove from heat and set aside.
Strain chicken mixture through a colander set over a bowl.
Return liquid to the pot and set solids aside.
Return liquid to a simmer, whisk in roux.
Simmer 3-5 minutes.
Stir half and half and peas into simmering liquid, then stir in the chicken mixture.
Season with salt and pepper.
Preheat oven to 350 degrees.
Roll and cut the puff pastry to cover one pie pan.
Pour filling into pan and top with dough.
Make two small slashes in the puff pastry to let the steam escape.
Bake 40-45 minutes, until the pastry is puffed high and golden brown.