In a heavy pot melt butter over medium heat. Add green onion, celery and garlic and sauté until soft.  Add artichokes then sprinkle mixture with flour and stir to coat well.

Gradually add stock, stirring constantly. Add cayenne, salt, Worcestershire and thyme and simmer, covered for 1 hour.

Add oysters, oyster liquid and sherry and simmer for 10 minutes. Do not allow soup to boil.

Stir in half and half and milk. Cool and refrigerate for at least 8 hours.

To serve, heat only the soup you plan to serve slowly over low heat.