01 - Heat a large pot over medium heat with butter or olive oil. Sauté the chopped onion until soft and translucent, about 5 minutes.
02 - Add the minced garlic and diced potato, stirring constantly for 2 minutes to coat and lightly toast.
03 - Pour in the vegetable broth and bring to a boil. Reduce the 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 vibrant green in color.
05 - Remove the pot from heat. Using an immersion blender, or working in batches with a countertop blender, purée the soup until completely smooth and velvety.
06 - Stir in the milk and season with ground nutmeg, salt, and black pepper. Gently reheat if necessary, but avoid boiling once the milk has been added.
07 - Ladle into bowls while hot. Garnish with a swirl of cream, croutons, and fresh herbs as desired.