- In a large pot over medium-high heat, soften the onion, celery and garlic in the butter. Add the remaining ingredients. Bring to a boil, then simmer for 15 minutes or until the vegetables are tender. Season with salt and pepper.
- In a blender, purée the soup until smooth. Adjust the seasoning.
- Meanwhile, with the rack in the middle position, preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper.
- Spread the Brussels sprout leaves on the prepared sheet. Drizzle them with the oil and season with salt and pepper. Roast for 8 minutes or until they begin to brown.
- When ready to serve, ladle the soup into shooter glasses and garnish with the Brussels sprout leaves and pomegranate seeds. Season with pepper and drizzle with olive oil, if desired.