How to Make It
In a small bowl, combine all of the ingredients. Sift through a fine sieve and store in an airtight container.
In a large, heavy pot, toss the onion with the olive oil and 1 teaspoon of salt. Cover and cook over moderately low heat, stirring occasionally, until the onion is very soft, about 10 minutes. Stir in the squash, cover with a round of parchment paper and the lid and cook for 20 minutes.
Add the tomato paste, 1 teaspoon of the spice blend and the water to the pot and bring to a boil. Reduce the heat and simmer until the squash is tender, 20 minutes. Let cool.
Working in batches, puree the soup in a blender; add the crème fraîche, three-fourths of the cheese and 1 teaspoon of harissa to the last batch. Return all of the soup to the pot and season with salt and black pepper. Serve the soup, passing the remaining cheese and more harissa at the table.