Heat the oil in a large saucepan over medium heat. Add the leeks, onions, and garlic, and cook, stirring, until they are tender. Add the reserved oyster liquid and cook 30 seconds. Add the heavy cream and potatoes; season with salt, white pepper, and black pepper to taste, the hot sauce, and Worcestershire sauce. Cook 4 minutes. Remove from heat and use an immersion blender to puree soup in the saucepan.
Return the saucepan to the heat. Add the milk and bring to a gentle simmer. Add the green onions, parsley and oysters. Cook just until the edges of the oysters begin to curl, about 2 minutes; be careful that oysters don't overcook. Remove from heat and add the butter, stirring until melted. Ladle the stew into 4 warmed shallow soup bowls and top with some croutons.
Yield: 4 servings