01 - Melt butter in a large pot over medium heat. Add leeks and onion, sauté for 5–7 minutes until soft but not browned.
02 - Add garlic, cook for 1 minute until fragrant.
03 - Add diced potatoes, bay leaf, and vegetable broth. Bring to a boil, then reduce heat and simmer uncovered for 20 minutes, or until potatoes are very tender.
04 - Discard bay leaf. Puree the soup using an immersion blender or carefully in batches with a blender until smooth and creamy.
05 - Return soup to pot if blended separately. Stir in heavy cream, salt, and pepper. Warm gently over low heat, but do not boil.
06 - Taste and adjust seasoning if needed. Serve hot, garnished with fresh chives.