In large skillet, melt butter over medium high meat. Add onion and cook for 4-5 minutes to soften.
Add salt, pepper, thyme, and rosemary. Add flour and stir together for 3-4 minutes.
Pour in milk and chicken broth, bring to a boil.
Reduce heat and add chicken Allow to cook for 15 minutes until chicken is cooked through and sauce has thickened.
If needed, make a slurry with 1 TBS corn starch and 1 TBS water and add to mixture to thicken.
Preheat oven to 375 degrees.
Turn off burner and add vegetables and stir.
Prepare puff pastry. Flour your work station and lay out a sheet of puff pastry. Using a rolling pin lightly roll pastry fold lines to prevent breakage.
Cut circles around 3 inches around. Using the rolling pin, roll circles until doubled in size.
Place circles onto a parchment linked baking pan. Place 2 TBS of pot pie mixture into center of a pastry circle. Place another circle on top of the mixture and seal edges with a fork. Continue until all pastry is filled.
Brush top and sides of pot pie pocket with the egg wash.
Crack black pepper over the pastry pockets.
Place pan in oven for 20-25 minutes until pastry puffs up and is golden.