Preheat oven to 450°. Pick herbs into 1-inch pieces and set aside.
In a medium bowl, stir mayonnaise and garlic together.
In a blender, combine coconut milk, turmeric, ginger, chile, shallot, and sea salt and blend on high.
Fill a large bowl with ice and water. Steam or boil the cauliflower until tender, about 10 minutes. Using tongs, transfer the cauliflower to the ice water to stop cooking. After the cauliflower has cooled, pat it dry with a paper towel and rub all over with garlic aioli.
Place romanesco in a heavy skillet and roast until lightly browned, about 45 minutes. Reduce oven to 350°. Spoon turmeric milk all over the cauliflower, sprinkle with pistachios and cook until deep golden brown, about 15 minutes. Place romanesco on a serving platter and sprinkle with herbs. Slice lengthwise into steaks and serve.