Step 1

To make the stock, heat half the oil in a large saucepan over medium heat. Add fennel seeds and cook, stirring, for 1 minute or until fragrant. Add celery, fennel, 1 carrot and half the onion, leek and garlic. Cook, stirring frequently, for 8 minutes or until carrot and fennel soften slightly. Add vinegar and 2.5L (10 cups) water, then bring to a simmer.

Step 2

Reduce heat to low and simmer for 45-60 minutes or until infused. Cool slightly. Strain through a fine sieve, discarding vegetables.

Step 3

Heat remaining 11/2 tbs oil in a large saucepan over medium heat. Add remaining onion, leek and garlic, and cook, stirring, for 2-3 minutes until soft. Add za'atar, cauliflower and remaining carrot, and cook, stirring, for 3-4 minutes or until warm. Add stock and bring to a simmer.

Step 4

Reduce heat to low, then simmer for 30 minutes or until vegetables are tender. Cool slightly, then, in batches, whiz in a blender until smooth.

Step 5

Divide soup among bowls and swirl through yoghurt. Serve topped with oregano, sumac, extra oil and za'atar.