In a large heavy stockpot, cook the bacon, stirring constantly, over medium-high heat until browned, about 5 minutes. Add the onion, stirring occasionally, and cook until soft, about 5 minutes. Add the garlic and cook for 1 minute, stirring constantly. Add the oysters, the oyster liquor, and the cream and bring the mixture to a boil. Remove the pot from the heat.
Using an immersion blender, or working with batches in a blender, puree the ingredients, adding the spinach in batches as you puree. Season with the salt and white pepper and stir in the Herbsaint.
Serve with the Crispy Brie Croutons.
Makes 2 quarts, 8 servings