Chef Duskie Estes rubs aromatic seasonings and tangy sumac all over heads of cauliflower, then roasts them whole. Slideshow: More Vegetarian Recipes
Preheat the oven to 450°. In a spice grinder, grind the first 8 ingredients to a powder. Brush the cauliflower with the olive oil and season generously all over with salt and pepper. Set the cauliflower in a 9-by-13-inch baking dish and rub with the spice mix. Add 11/2 cups of water to the dish. Roast for 1 hour, or until tender and browned; add more water if necessary.
In a blender, combine the first 6 ingredients and puree until very smooth. Season with salt.
Serve the cauliflower whole, or cut into thick slabs and arrange on a platter. Garnish with parsley and serve with the tahini sauce.