Cook celery, onion, and bay leaf in margarine or butter in a 4-quart Dutch oven or large saucepan over medium-high heat for 4 to 5 minutes or until vegetables are tender. Reduce heat to low; add spinach, green onion, and parsley. Cook, stirring constantly, for 4 minutes. Remove bay leaf.
Add garlic, thyme, oregano, salt, and black, red, and white peppers. Cook, stirring constantly, for 4 minutes. Add flour and cook for 2 minutes, stirring constantly and scraping the sides and bottom of the Dutch oven or saucepan.
Drain oysters, reserving liquid; if necessary, add enough chicken broth to oyster liquid to make 1 cup total. Set aside.
Increase heat to medium-high and carefully add Herbsaint or Pernod to vegetable mixture. Cook, stirring constantly, for 4 minutes. Add oyster liquid and cook, stirring occasionally, for 4 minutes. Cool slightly. Transfer vegetable mixture to a blender container or food processor bowl. Cover and blend or process until smooth.
Return mixture to the Dutch oven or saucepan. Stir in whipping cream. Cook and stir over medium heat for 4 to 5 minutes, or until heated through, whisking occasionally. Add oysters and cook, stirring occasionally, about 5 minutes or until oyster edges curl. Serve immediately. Garnish with sprinkling of cracked red peppercorns, if desired. Makes 12 appetizer servings.