For the spinach, in saut pan over medium heat, melt butter. Add garlic and onion, and cook until soft. Add spinach and saut until soft. Add heavy cream and nutmeg. Cook until slightly reduced and thickened, but still liquidly. Remove from heat; fold in cream cheese. Set aside and allow spinach to cool completely.
Preheat oven to 325F.
Spread bread cubes on a baking pan and bake until golden brown, stirring occasionally, about 25 minutes. Remove and let cool. Once cooled, place in a mixing bowl.
In large saut pan over medium heat, add olive oil. Cook onions, celery and carrots; deglaze with vermouth and reduce. Add butter and remove from heat. Transfer vegetables to bowl with bread pieces, add chicken stock and mix. Fold in creamed spinach, oysters and oyster liquid, and herbs, and mix thoroughly. Season with salt and pepper to taste.
Transfer to a buttered baking dish and bake covered at 325F for 30 minutes. After 30 minutes, remove cover and bake for an additional 25 minutes until golden brown.