Add the carrots, onion and garlic to a sheet pan/tray and spread out evenly. Drizzle with vegetable oil and an even sprinkling of salt, white pepper and cumin, mix until coated. Roast in the oven for 35 minutes until tender. To a large saucepan add the vegetable stock and bring to a simmer. Add the carrots, onions, garlic squeezed out of its peel, ginger and bay leaf. Simmer for 15 minutes.
Remove the bay leaf. Using an immersion blender, or add to a blender in batches, blend soup until it is smooth and reaches the desired consistency, if it is too thick, add more stock.
Check for seasoning and adjust to your taste.
Serve garnished with chopped fresh chives and sour cream.