you could also make this with cooked real chicken and normal chicken broth. this is a nice mild soup for spring or summer. serve with fresh, not-sweet bread and a mojito or chilled white or rose wine.
cut off most of the green ends of the leeks and slice in half lengthwise, leaving the root end intact to keep them all together. chop into 1/2 inch slices and toss in a strainer, wash well to break up and get rid of sand/dirt.
chop celery and mushrooms, mince garlic, and combine with leeks, water, broth cube, and spices in a stock pot.
bring to a boil and simmer for about 10-15 min or until leeks and celery are soft. in the mean time dice up the "chicken".
add "chicken" and rice, simmer until rice is cooked, about 5-10 min.
mix corn starch with cold cream and add to soup, stirring well.