Preheat your oven to 425°F (220°C). Cut the cauliflower into bite-sized florets and place them on a baking sheet. Drizzle with olive oil, then season with kosher salt and black pepper. Roast for about 25-30 minutes, turning halfway, until golden brown and tender.

In a large pot, heat a tablespoon of olive oil over medium heat. Add the chopped onion and sauté for 6-7 minutes until translucent. Add minced garlic, cumin, paprika, sumac, and turmeric, cooking for another minute.

Add the roasted cauliflower to the pot, mixing well with the onions and spices. Pour in the vegetable broth and water, bringing the mixture to a boil, then reduce to a simmer for 5-7 minutes.

Using an immersion blender, carefully purée the soup to desired smoothness. For a chunkier texture, blend partially.

Lower the heat, stir in the milk and lemon juice, warming gently for 2-3 minutes. Adjust salt if necessary, and fold in some reserved roasted cauliflower.

Serve the soup in bowls, garnished with fresh dill and optionally a drizzle of olive oil. Enjoy with warm pita or Greek salad.