Simmer the potatoes in the clam liquid until nearly cooked through. Strain and reserve the potatoes and the liquid.
While the potatoes are simmering, heat the butter in a large heavy-bottomed pot. Add the onions, celery and carrots, and sweat until translucent, about 3 minutes.
Add the flour and cook until slightly golden.
Add the clam liquid to the roux, whisking away any lumps.
Add the thyme and simmer for about 20-25 minutes or until the carrots are tender.
Using a ladle, temper the cream to prevent curdling (remove some of the soup and add it to the cream in a liquid measuring cup. Then pour it back into the soup)
Add the clams and potatoes, and season to taste with salt, pepper, Tabasco sauce and Worcestershire sauce. Remove the thyme.
Garnish each serving with fresh parsley.