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 lightly coat and begin softening.
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. Blend soup with immersion blender until completely smooth and creamy, or blend in batches using a countertop blender.
05 - Return to low heat. Stir in milk and cream, then gradually add grated cheddar. Heat gently, stirring constantly until cheese is fully melted and incorporated.
06 - Taste and adjust salt and pepper as needed. Serve immediately in warmed bowls, garnished with fresh chives and additional cheddar if desired.