Preheat oven to 375°F/190°C.
Add the carrots, onion and garlic to a baking sheet and spread them out evenly.
Drizzle with the vegetable oil and sprinkle with the salt, white pepper and cumin. Toss to coat.
Roast for 35 minutes, or until the carrots are tender.
Meanwhile, add the vegetable stock to a large saucepan and bring to a simmer.
Add the roasted carrots and onion, squeeze the roasted garlic out of its peel, and add it to the saucepan along with the ginger and bay leaf. Simmer for 15 minutes.
Remove the bay leaf. Blend the soup until smooth using an immersion blender, or carefully transfer it to a blender in batches. If the soup is too thick, add more stock until it reaches your desired consistency.
Taste and adjust the seasoning as needed.
Serve garnished with plant-based sour cream and chopped fresh chives.