Preheat oven to 425. Defrost one pie crust (if using)
Cook:
1 c sliced carrots
1/2 c sliced celery
in
2.25 c water
1.5t chicken base
until mostly cooked.
[optional: 8 oz sliced mushrooms. Probably best to cook them in a little oil until they've sweated out a good deal of liquid; if so, use 2.25c stock above. If not (i.e., if they're raw), reduce to 2c stock]
Add
1 c frozen green peas
and cook until they're warmed through.
While that's cooking, cut into cubes
1 lb cooked chicken breast (or up to "all the meat on a store-bought roasted chicken")
In a larger saucepan, cook
1/3 c chopped onion (about 1/2 medium onion; OK to use more)
in
1/3 c butter
with
1/2 t salt
1/4 t pepper
1/4 t celery seed
until onion is translucent.
Whisk in
1/3 c flour
and cook until no longer raw, but not browned.
Add
2/3 c milk
bit by bit, whisking, and
the liquid from the vegetables
whisking, and simmer over medium heat until it's thickened quite a lot.
Put
1 prepared pie crust [if using]
into a suitable dish. Lay out
chicken and
veg mix
atop it and spread evenly. Pour the roux over it and spread evenly.
Top with
a prepared pie crust, OR
a rolled-out puff-pastry crust
and poke holes to vent steam.
Bake for 30-35 min, or until pastry is golden brown and filling is bubbly.