Slice mushrooms to make 3 cups.  Place remaining caps and all stems in a 2 1/2 quart saucepan with the stock.  Bring to a boil, then simmer for 30 minutes.

In a 5 quart saucepan, heat oil over medium heat.  Add celery, leaks, and garlic.  Season with salt and pepper.  Saute for 5-8 minutes.  Add stock; simmer.

In a 2 1/2 quart saucepan, melt butter on low heat.  Add flour.  Cook roux until bubbly (6-8 minutes), stirring constantly.  Strain 4 cups of stock into the roux; whisk until smooth.  Return all to the large pot.  Simmer for 20 minutes.

Heat 1 tablesoon of butter over medium heat.  Add remaining sliced mushrooms and saute for 4 minutes.  Add tomatoes and cook for 4 minutes.  Add cream.  Add to soup.  Adjust seasonings with salt and pepper.  Serve.