In a stockpot, combine chicken and stock. Heat to a boil and, after five minutes, skim off any impurities. Add the mirepoix, bay leaves, and season, to taste. Cover and cook until fork-tender, about 1 1/2 hours. Remove the chicken and strain the stock, reserving the liquid.
Meanwhile, combine flour, salt, baking powder, and parsley in a bowl. Cut in butter with a fork until the mixture resembles coarse meal. Add 10 ounces milk and stir briefly with a fork. Add only enough of the remaining 2 ounces of milk to make the dough hold together. Roll dough out to 1/4-inch thickness. Cut dough into 2-inch rounds.
Heat 2 quarts of the strained stock to a boil, reduce heat to a simmer, and drop in the dumplings. When they rise to the top, cover and simmer for 10 minutes or until they are cooked inside. Keep warm.
Combine the canola oil and flour, and heat together until light brown in color (blond roux). Add some hot stock to the roux, to loosen it, and then add the roux to the simmering 1-quart of stock. Heat to a boil, then reduce heat and simmer for about 10 minutes or until the starch is fully cooked and mixture is smooth. Strain the sauce through a fine strainer and keep warm.
Meanwhile, cut the chickens into quarters and partially debone.
To serve, place a portion of chicken on a preheated dinner plate, arrange dumplings around chicken and cover (nappe) with sauce.