Preheat the oven to 400 degrees F.
Carefully unfold one sheet of puff pastry
on a floured surface. Using a rolling pin
, roll out the pastry large enough to cover the bottom of 9-inch pie plate
with overhang (about 12 inches in diameter). Trim the overhang, and using the tongs of a fork, prick the bottom of the pastry all over.
In a saucepan
over medium-high heat, melt
the butter. Add the carrots, celery and onions
and cook until the vegetables start to soften, about 5 minutes. Stir in the flour and cook for 2 minutes, stirring constantly. Slowly add the broth and milk
. Bring to a boil, reduce to a simmer
and cook until the mixture thickens enough to coat the back of a spoon.
Stir in the turkey
, peas, celery seed and season with salt and pepper. Remove from the heat and cool completely.
Unfold an additional sheet of pastry on a floured surface and cut into 6 to 8 even strips.
Pour the filling into the pie crust
. Create a lattice pattern over the top by weaving the strips over and under each other. Trim the excess edges. Gently beat the egg and 1 tablespoon water in a small bowl. Brush the dough
with the egg wash
before placing the pot pie
on a sheet tray.
Place in the oven and bake until the pastry is golden brown and the filling is bubbly, 45 minutes. Cool for 10 minutes before serving.