Heat your oven to 200C/Fan 180C/Gas 6. Pull the leaves off the cauliflower. Break it into florets. Tip into a bowl. Drizzle with 1 tbsp olive oil and season with salt and pepper. Spread out on a baking tray. Roast for 35 mins till the cauliflower is tender and golden.
While the cauliflower roasts, peel and finely chop the onion and potato. Warm a large pan over a low heat for 1 min. Add ½ tbsp oil. Add the onion and potato. Season. Cover and sweat over a low heat for 10 mins till the veg have started to soften. Stir now and then.
Add most of the thyme sprigs to the veg in the pan. Crumble in the stock cube and add 800ml boiling water (or just use 800ml hot homemade stock). Bring to the boil. Turn the heat down and simmer for 10 mins till the veg are soft.
Scoop the thyme sprigs out of the pan with a fork. Lift the cauliflower off the tray and add to the pan. Simmer together for 5 mins to get the flavours to mingle. Lade into a blender and blitz until smooth, or use a hand-held blender. Taste and add more salt and pepper if you think it needs it. Serve in warm bowls, topped with the dukkah and the last of the thyme leaves.