Put the olive oil, garlic, and shallot in a deep pot over medium heat. Cook for a few minutes, or until the garlic turns golden in color. Add the tomato puree, and chestnuts, and cook for another minute. Add the vegetable stock and bring the soup to a boil. Season the soup with salt and pepper, to taste. Reduce the heat, and let simmer for about 40 minutes. Before serving in individual bowls, sprinkle the soup with chopped parsley and croutons.