Step 1
From the cauliflower head, cut 1 cup of small florets and reserve. Coarsely chop the remaining cauliflower, including stem and core.
Step 2
Heat 1 tbs of oil in a large heavy saucepan over medium heat. Add the chopped cauliflower, onion and 2 tsp salt. Cover. Cook, stirring occasionally, for 15 mins or until onion softens. Add 5 cups (1.25L) of water and cook, covered, for 15 mins or until cauliflower is completely tender. Cool, then transfer to a blender and carefully blend until completely smooth. Season with salt. Reheat. Keep warm until ready to serve.
Step 3
Meanwhile, preheat oven to 200°C (180°C fan-forced). Line a baking tray with baking paper. Arrange 8 equal mounds of parmesan, about 4cm apart, on prepared tray. Use the back of a spoon to flatten mounds to even thickness, about 8cm in diameter. Bake for 6 mins or until parmesan melts and is pale golden. Cool on tray until crisp. Sprinkle with pepper. Transfer to a bowl and break into breadcrumb-sized pieces.
Step 4
Heat remaining 1 tbs oil in a large heavy frying pan over medium-high heat. Add reserved cauliflower florets and cook, tossing frequently, for 4 mins or until cauliflower is heavily browned. Transfer to a plate lined with paper towel and sprinkle with salt.
Step 5
Ladle soup into serving bowls and garnish with cooked florets, parsley, parmesan crumbs and lemon zest. Grind black pepper over each bowl to serve.