Start with the crust by putting flour, baking powder and salt in a food processer until the ingredients are combined. Add butter, one piece at a time. Separate the egg and refridgerate the egg white. Add the yolk and milk to the food processor and pulsa it until the dough comes together. Put it out on a lightly floured surface and flatten it into a disk, wrap it in plastic and refrigerate it for at least an hour.
Preheat the oven to 425 degrees. Prick the potatoes with a fork and bake them directly on the oven rack until tender, which takes about 45 minutes. Cool them slightly, then break them into small pieces.
Add the chicken broth, carrots, and thyme to a simmer in a saucepan. In a separate pot, heat the olive oil and add the onions to cook until they’re soft for about 8 minutes. Sprinkle in the flour and stir until lightly toasted. Then, add milk, celery, potato pieces, and the warm broth mix. Let it simmer until it thickens for about 15 minutes.
Remove the pot from the heat and add the chicken, yogurt, peas, and parsley. Season it with salt and pepper.
Transfer the filling from the pot into the casserole dish. Get the dough and roll it out on the lightly floured surface until it is slightly larger than the dish. Get the egg white out and brush it over the dough and add salt and pepper on top.
Press the dough against the sides of the dish and put it in the oven. Bake it until the crust is golden brown, for about 20 minutes.
Calories 482; Fat 19 g (Saturated 8 g); Cholesterol 137 mg; Sodium 795 mg; Carbohydrate 47 g; Fiber 5 g; Protein 31 g