2) Add in 220g of the cold butter, 4 tbsp at a time, pulsing after each addition until mixture forms coarse texture. Slowly add 6 to 8 tbsp water with the machine running, 2 tbsp at a time, until the dough balls up to one side.
3) Remove the dough onto a lightly floured board, cut in half and form into 2 (16cm) rounds. Wrap each tightly with cling film and place in the refrigerator. Chill for 30 minutes prior to rolling out. Repeat to make a second batch of dough.
For the filling:
1) In large saute pan, melt the butter over a medium heat; add the onions, shallot and celery and saute until just starting to brown.
2) Stir in the flour and saute for 2 minutes. Slowly whisk in the hot stock, stirring well, until the sauce is bubbly and thickened, about 5 to 6 minutes.
3) Stir in the chopped chicken, carrots and peas, and sage. Season, to taste, with salt and pepper. Remove from the heat and leave to cool while rolling out the pastry.
To assemble the pot pies:
1) Preheat the oven to 180C/Gas 4. On lightly floured board, cut the rounds of dough in half. Roll the pieces into 12cm rounds, about 0.5cm thick.
2) Place a round in the bottom of each aluminium pie tin and lightly press the sides and bottom to fit the shape of the tin. Generously top with filling until full and slightly mounded.
3) Top with a second piece of crust and pinch the seams together. Cut 2 small slits in the top of each pie. Brush with egg wash, place on a baking sheet and bake for 1 hour to 1 hour 15 minutes or until the tops are golden brown and the filling is bubbling.