01 - Heat a large pot over medium heat and add butter or olive oil. Sauté the finely chopped onion until soft and translucent, approximately 5 minutes.
02 - Add the minced garlic and diced potato, stirring continuously for 2 minutes to coat evenly.
03 - Pour in the vegetable broth and bring to a boil. Reduce heat and simmer for 10 minutes until the potato is fork-tender.
04 - Add the fresh spinach and cook for 2 to 3 minutes until fully wilted and bright green in color.
05 - Remove from heat. Using an immersion blender or a countertop blender in batches, purée the soup until smooth and velvety in texture.
06 - Stir in the milk and season with ground nutmeg, salt, and black pepper. Gently reheat if necessary, but do not bring to a boil after adding the milk.
07 - Ladle into bowls while hot. Garnish with a swirl of cream, croutons, and fresh herbs as desired.