Place 100g (¾ cup) of cashews and 1 cup (250ml) boiling water in a heatproof bowl and allow to soak for 1 hour.
Preheat the oven to 220˚C (200°C fan forced) Place remaining cashews on a baking paper lined tray and toast in oven for 3 minutes, remove and set aside.
Place potato in a saucepan of cold water. Bring to the boil over high heat, then reduce to a simmer and cook for 10 minutes or until just tender. Drain and place in a large roasting pan.
Place cauliflower in a microwave-safe bowl, add 2 tablespoons water and cover with plastic wrap. Microwave on high for 8-10 minutes or until tender. Cool slightly, then cut in to quarters and add to potatoes. Combine 1 ½ tsp of turmeric and cumin with 2 tablespoons of oil. Pour over combined vegetables and gently toss to coat. Season well with salt and pepper. Roast for 30 minutes.
Heat remaining 2 tablespoons of oil in a medium sized saucepan over medium heat. Add onion, celery and garlic to pan and cook stirring occasionally, for 4-5 minutes or until turning brown. Add chilli, coriander stalks and remaining 1 ½ tsp of turmeric and cumin, and stock cook, stirring constantly, until simmering. Drain cashews, add to the sauce then using a stick blender, puree until smooth.
Serve roasted vegetables in cashew sauce. Scatter over coriander leaves and toasted cashews.
Other optional sides include rice, flaked coconut and Indian flat breads.