Preheat oven to 400°F.

Quarter the cauliflower. Using a mandolin or sharp knife, thinly shave two quarters (excluding the stem). Add to a bowl with a pinch of salt, a squeeze of lemon, and half the chives. Toss and set aside.

Trim florets from the remaining two quarters. Reserve stems. Toss florets with olive oil and salt. Roast for 8–10 minutes until golden brown.

Roughly chop the reserved stems, onion, and garlic. Add to a medium pot with a splash of oil and cook over medium heat for 4–5 minutes.

Cover with water and bring to a boil. Simmer for 20 minutes, stirring occasionally, until tender. Transfer to a blender and purée until smooth. Season with salt and lemon juice to taste. If purée is too thin, return to pot and reduce slightly.

To plate: spread purée on the base of the plate, top with roasted florets, then the marinated shaved cauliflower. Finish with maldon salt and remaining chives.