In a large pot, melt the butter and gently sauté the onion until soft, about 10 minutes.
Add the cauliflower, potato, nutmeg, stock, a generous grind of black pepper, and a teaspoon of sea salt. Let it simmer for about 25 minutes or until the vegetables are tender.
Once cooked, blend the mixture until smooth using an immersion blender. We recommend the Bosch Stick Blender for best results.
Check the seasoning and adjust according to taste.
To serve, ladle the soup into warmed bowls. Sprinkle za'atar and some freshly ground black pepper on top. Accompany with toasted bread dices for that added crunch.