In a large pot, melt the butter over medium heat. Add the onion, celery and garlic and cook, stirring occasionally, for 5 minutes until the onions are transparent.

Add the chopped potato, vegetable broth, rosemary, and kosher salt and bring to a simmer. Simmer for 10 minutes until the potatoes are tender.

Add the spinach and simmer 5 minutes more until the spinach is wilted and the potatoes are very tender.

Carefully transfer the hot soup to a blender using a ladle. Blend until creamy and pureed. Add the heavy cream and pulse to combine.

Taste and add 1 to 2 more pinches salt. Serve warm, garnished with a drizzle of cream.