Chicken Pot Pie in a Pocket

For the dough, pulse-process flour, butter, salt and sugar in food processor. While pulsing the machine stream in eggs and just enough water for the dough to come together. Turn dough out onto a floured work surface, knead a couple of times then wrap in plastic. Chill 1 hour. 
 
Place chicken in a saucepot with salt, peppercorns, bay, onion, herbs, stock and enough cold water to cover. Poach at a low simmer until cooked through, 20 minutes. Remove from heat and let cool in the poaching liquid. Remove skin and pull the meat from the bones; discard carcass and strain the stock.

 
Preheat oven to 375°F.
 
Heat a sauté pan over medium heat and melt butter. Cook celery, carrots, leeks and potato to tender, season with salt and pepper. Add flour and stir to combine, add 1 1/2 cups poaching liquid and thicken. Add tarragon, pulled chicken meat and peas, and heat through; let thicken a bit more. Remove pan from heat and let cool. 
 
Roll out pastry and cut into 6 rectangles that are 6x8 inches in diameter. Place filling on a triangle-shaped half of each square and press edges; arrange turnovers on a baking sheet lined with parchment. Brush turnovers with egg wash and bake to golden and hot through.