01 - Melt butter in a large pot over medium heat. Add leeks, onion, and garlic. Sauté for 5–6 minutes until soft and fragrant, avoiding browning.
02 - Add diced potatoes to the pot and cook for 2–3 minutes, stirring occasionally to coat with butter and aromatics.
03 - Pour in vegetable broth, salt, pepper, and nutmeg. Bring to a boil, then reduce heat and simmer uncovered for 20–25 minutes until potatoes are completely tender.
04 - Remove from heat. Purée using an immersion blender until smooth and creamy. Alternatively, blend in batches using a countertop blender and return to pot.
05 - Stir in milk and heavy cream. Add grated cheddar cheese and heat gently, stirring constantly until cheese melts completely and soup achieves velvety consistency.
06 - Taste and adjust seasoning with additional salt and pepper if needed. Serve hot, garnished with fresh chives and extra cheddar if desired.