In case you need to sub a few things: In place of green onions you can use leeks, or yellow or white onion. For the spinach, you can sub with kale. You can use frozen spinach if you don't have fresh on hand.If you want a sub for parsley, I’d suggest a fresh herb that you favor, such as chervil, basil, cilantro or tarragon—keeping in mind that these alternative herbs will change the flavor.As for substituting truffle salt, you can use any salt you favor, such as a fine sea salt.One last note—I usually use water for this soup because it’s easier and I don’t always have vegetable broth on hand.
Preheat your oven to 400°F (200°C or gas mark 6) and line a baking sheet with parchment paper or a non-stick baking mat.
Mix together the diced cauliflower and garlic with 1 tablespoon of oil and 1/8 teaspoon salt and spread it across the prepared baking sheet. Bake for 20 minutes or until the cauliflower begins to brown on the edges.
While the cauliflower is baking, heat a large saucepan on a medium heat and add 1 tablespoon of olive oil to it.
Add the onions and zucchini to the saucepan and cook for 10 minutes or until the zucchini begins to soften and brown a bit.
Add the cauliflower and 4 cups of vegetable broth or water to the onions and zucchini and bring to a low boil. Simmer for 10 minutes or until the zucchini are tender.
Turn the heat off and add the spinach and parsley to the saucepan. Let the greens sit for a few minutes, or until they are wilted.
Add the truffle salt and lemon juice and stir the soup to blend well.
Using a blender, and immersion blender, or food processor, purée the soup in batches until it’s all well-blended and creamy.
Serve warm, or cold, or store in the refrigerator for a few days or freeze for a few months.