Place the dried porcini mushrooms into a small bowl and cover with hot water. Set aside to allow to reconstitute until soft. Reserve the liquid and slice the mushrooms.
Meanwhile, warm the chicken stock in a small pot.
Melt the butter in a medium pot over medium-high heat.
Add the onion and celery and saute for 5 minutes.
Add the sliced mushrooms and cook another 10 minutes.
Add the flour and stir. The mixture will get thick.
Reduce heat to low and cook for 10 minutes.
Stir in the warmed chicken stock, the liquid from the reconstituted porcini mushrooms, and the heavy cream..
Season with salt and pepper to taste.
Bring to a simmer and let simmer for 30 minutes, stirring occasionally.
Serving: There are a lot of mushrooms in this soup. They are needed to give it such a fantastic mushroom flavor, but if you find them to be too much in the soup, just serve the creamy liquid portion with as little or as much of the mushroom 'meat' as you wish. We enjoyed the soup served both ways, with or without the mushrooms.