Step 1

Heat the oven to 450 degrees. Sit the cauliflower head on its side and trim the stalk flush with the bottom of the head, leaving any ribs and leaves that stay on. Using a paring knife, pierce the blade straight down into the center of the stalk. Remove the knife and pierce the stalk again to make a plus sign.

Step 2

Fill a medium pot with ½ inch of water and bring to a boil over high heat. Season the water with salt, then place the cauliflower head, stalk side down, in the water and cover the pot. Without reducing the heat, steam the cauliflower for 10 minutes. Uncover and use a spider or two spatulas to transfer the cauliflower to a cutting board. Turn it over and check to see if the tip of your knife can slip easily in and out of the side of the stalk. If not, return it to the water until it does.

Step 3

Place the cauliflower, stalk side up, on a rimmed baking sheet, then pour 1 tablespoon of the oil over the cauliflower, rubbing it in with your hands. Flip the cauliflower over and pour over the remaining 1 tablespoon olive oil. Rub the cauliflower with the oil so it's well coated. Season the cauliflower liberally with salt and pepper, then place the baking sheet in the oven and roast the cauliflower until it's blackened at the floret edges and crisp all over, 1 hour 15 minutes.

Step 4

Meanwhile, make the sauce: Heat the cumin seeds and chile flakes in a small skillet over medium heat, tossing occasionally, until fragrant and toasted, 3 to 4 minutes. Transfer the spices to a spice grinder, let cool for a couple of minutes, then process until finely ground. Transfer the ground spices to a medium bowl.

Step 5

Use a Microplane zester to grate the garlic into the bowl, then use the zester to remove the zest from 1 lemon, letting it fall into the bowl. Juice both of the lemons and measure out 6 tablespoons; save any extra juice for another use. Pour the juice into the bowl along with the tahini and soy sauce, then whisk everything to combine. If the sauce is too thick to pour (depending on the brand of tahini you use, this can happen), whisk in 1 tablespoon hot tap water (and up to 3 tablespoons) until it's loose enough to pour. Season the sauce with salt and pepper.

Step 6

When the cauliflower comes out of the oven, immediately pour half the tahini sauce over the cauliflower so it enrobes it fully. Sprinkle liberally with sesame seeds and parsley and serve immediately, with the rest of the tahini sauce on the side.