In a 2 quart saucepan, melt 4 tablespoons butter over low heat. Add the nutmeg and cinnamon and cook for 1 minute. Sprinkle the flour over the butter, and with a wooden spoon, stir to blend.
Increase the heat to moderate and slowly add the chicken stock, blending well after each addition so that there are no lumps. Mix in the cream, salt and pepper.
Gradually bring the mixture to a boil, stirring constantly. When it has thickened, add the prunes and currants. Cook over low heat 10 minutes.
Meanwhile, melt the remaining 4 tablespoons of butter in a saut^B pan over moderately low heat. When it foams, add the mushrooms and peppers. Sauté until soft, about 5 minutes. Add the onions, increase the heat to moderate, and sauté for 15 minutes, stirring occasionally.
Preheat oven to 375° F. Place the chicken in a large mixing bowl. Scrape the sautéed vegetables and peas on top, then pour the prune sauce over all.
Toss gently to distribute all the ingredients. Taste for seasonings and adjust if needed. Spoon the chicken mixture into a deep 4-5 quart ovenproof casserole.
Roll out the flaky pastry or puff pastry and, using the casserole's lid as a guide, with the tip of a sharp knife cut it to fit. Lay the pastry over the chicken mixture and brush it with the egg wash.
Bake for 60-70 minutes, or until the pastry is golden brown. Serve immediately.Servings: 10 to 12