Burning the leek in this recipe lends an aromatic charred note, adding balance to the raw and poached cauliflower.
- 1 medium leek, white and pale-green parts only, halved lengthwise
- 1 small head of cauliflower, cut into large florets, trimmings reserved
Preheat oven to 500°. Set vents to high and open a window for adequate ventilation. Place leek on a foil-lined baking sheet. Roast until blackened, dry, and crisp, 70-90 minutes. Let leek cool. Break into shards. DO AHEAD: Leek ash can be made 3 days ahead. Store airtight at room temperature.
Using a mandoline, thinly slice 3 large cauliflower florets lengthwise (reserve trimmings); set aside.
Bring milk and 1 cup cauliflower trimmings to a boil in a large saucepan; reduce heat and simmer until cauliflower is tender, 20-25 minutes. Let cool slightly, then transfer cauliflower mixture to a blender or use an immersion blender in the pan and purée until smooth.
Return cauliflower purée to saucepan, add remaining cauliflower florets, and season with salt. Simmer until florets are just tender, 8-10 minutes. Using a slotted spoon, transfer florets to a medium bowl (rinse off any purée on florets).
Strain purée into another medium bowl. Divide florets among shallow bowls; spoon purée over. Garnish with reserved cauliflower slices; sprinkle with leek ash.