Preheat oven to 220°C with rack in centre position with clean roasting pan inside
Cut up cauliflower into medium/large florets & place in large bowl with oil, salt, chilli flakes. Gently toss until evenly coated
Place in hot prepared tray - they should sizzle a bit on contact
Use tongs to arrange the florets so they are not touching, cut side down if you can
Roast for 25 mins, flipping halfway, until deeply brown & just tender
Combine all sauce ingredients except salt & pepper in a small bowl, add 1 tsp water & whisk to loosen
Season to taste
Spoon the sauce onto the plate, gently place cauliflower on sauce and serve