Clean leeks and cut into 1 cm pieces. Steam in half cup water until tender. Do not drain. Set aside. Melt butter in saucepan. Add flour to make a roux. Cook 2 to 4 minutes. Add chicken stock, stirring with wire whip, bring to boil. Turn heat on low and add remaining ingredients. Do not boil. Add 1 cup diced, cooked potatoes and 1 cup diced, cooked ham, if desired.