01 - Melt butter in a large pot over medium heat. Add chopped onion, garlic, and leeks. Cook, stirring occasionally, until softened but not browned, about 6-8 minutes.
02 - Add diced potatoes, bay leaf, and thyme. Stir to combine for 1 minute to release herb flavors.
03 - Pour in vegetable broth and water. Bring to a gentle boil, then reduce heat. Cover and simmer for 20-25 minutes until potatoes are completely tender.
04 - Remove bay leaf. Using an immersion blender, puree soup until smooth and velvety. Alternatively, carefully transfer in batches to a countertop blender.
05 - Stir in heavy cream. Warm gently over low heat without boiling. Season generously with salt and pepper to taste.
06 - Ladle into warmed bowls and garnish with chopped fresh chives or parsley if desired.