Heat the olive oil in a large pot or Dutch oven over medium heat. Add the chopped onion and cook, stirring occasionally, until softened and translucent, about 5-7 minutes.

Add the minced garlic and cook for another minute until fragrant, being careful not to let it burn.

Add the cubed potatoes and vegetable broth to the pot. Increase the heat to high and bring to a boil.

Once boiling, reduce the heat to low, cover, and let it simmer for 15-20 minutes, or until the potatoes are very tender and can be easily pierced with a fork.

Remove the pot from the heat. Add the fresh spinach in handfuls, stirring it into the hot soup until it wilts completely. This should only take a couple of minutes.

Use an immersion blender to carefully blend the soup directly in the pot until it is smooth and creamy. Alternatively, transfer the soup in batches to a countertop blender and blend until smooth (see notes for blender safety).

Return the blended soup to the pot (if using a countertop blender). Stir in the heavy cream, salt, black pepper, and freshly grated nutmeg.

Place the pot over low heat and warm the soup gently, being careful not to let it boil. Taste and adjust seasoning if necessary.

Ladle the hot soup into bowls. Garnish with croutons, fresh parsley, or a drizzle of olive oil or cream, if desired, and serve immediately.