Let the spinach thaw. Peel and finely chop the shallot and garlic. Peel the potato and cut into cubes.
Heat the oil in a pot. Fry shallots and garlic in it over medium heat for about 1 minute until translucent. Add the potato cubes. Pour in the broth, bring everything to a boil, cover and cook gently for 10 minutes over a medium heat. Stir in the spinach and 1 tablespoon crème fraîche, bring to the boil again and cook uncovered for another 4-5 minutes. Puree with the blender. Season the soup with nutmeg, salt and pepper. Spread on soup bowls and garnish with the remaining crème fraîche.