Heat the oven to 375°F and place a rack in the middle position.
Grab the cauliflower head and trim away the leaves at the bottom of the cauliflower head. Carefully cut off and remove the stem and tough core, but be careful to keep the head intact.
In a large bowl, whisk coconut milk, tandoori spice, lemon juice, and ½ teaspoon Diamond Crystal kosher salt. (Got a bottle of Tandoori marinade? Simply measure out ½ a cup of it.)
Place the cauliflower head bottom side up in the dish or pan you are going to roast it in. Pour some of the tandoori marinade all over the bottom of the cauliflower and use a pastry brush to paint it evenly on the surface.
Flip the cauliflower over and pour the rest of the tandoori marinade over the top and paint the top until it is completely covered.
Cover the pan tightly with aluminum foil. (You can also put a layer of parchment between the foil and cauliflower if you prefer.)
Put the skillet on the middle rack in the oven. Cook for 30 minutes, covered.
Remove the foil from the skillet. Baste the top of the cauliflower with the sauce in the pan and roast for an additional hour in the oven, uncovered. Once the cauliflower is golden brown on the outside and tender on the inside, take it out of the oven.
Transfer the cauliflower head to a cutting board or platter and sprinkle with your favorite flake finishing salt for crunch and salinity!