Step 1

Arrange an oven rack in the center of the oven and preheat to 475 degrees F.

Step 2

Trim the stem of the cauliflower, keeping the leaves intact, so it will sit level on a rimmed baking sheet. Bring 2 gallons of water to a boil in a large stockpot over high heat. Stir in 6 1/2 tablespoons of the sel gris until dissolved.

Step 3

Brush a rimmed baking sheet with olive oil; set aside.

Step 4

Add the cauliflower to the water and boil until tender and a fork inserted in the cauliflower meets no resistance, 12 to 13 minutes. Using a spider or 2 slotted spoons, gently lift the cauliflower from the water and let drain, allowing the water to drip back into the pot.

Step 5

Place the cauliflower, stem-side down, on the prepared baking sheet. Brush olive oil over the cauliflower in a thin, even layer. Sprinkle the remaining 1 1/2 teaspoons sel gris over the cauliflower (the salt might clump in some places). Bake until browned, 35 to 45 minutes. Remove from the oven, cut into thick wedges and serve hot.