Remove liquid from the refrigerator and remove fat which has risen to the top. Clean the leeks, then chop them into small round sections. In a large pan, melt the butter. Add leeks and scallions. Cover with a tight-fitting lid, and sweat over medium heat for 5 minutes, shaking to rotate. Slowly add all the stick, then the chicken pieces. When you are ready to serve, bring slowly to a boil and simmer for 15 minutes. Stir well, then add salt and pepper to taste. To serve, sprinkle each portion with a teaspoon of the parsley.