Heat your oven to 200°C/Fan 180°C/Gas 6. Rinse the rice with cold water and set aside. Cut the cauliflower into small florets. Trim the roots and dry ends off the leek and finely slice it.
Pour 2 tbsp oil into a shallow ovenproof casserole dish or roasting tin. Slide it into the oven to heat for 2 mins. Add the cauliflower and leek to the casserole dish. Toss to coat in the oil. Sprinkle in a little salt and pepper. Roast for 20 mins.
While the veg roast, peel and finely grate the ginger. Halve the chilli, flicking out the seeds and membrane for less heat, and finely chop it. Crumble the stock cube into a heatproof jug. Add the ginger and chilli, along with the bay leaf, cinnamon stick, cloves and curry powder. Add the boiling water to the jug and stir.
Turn the oven down to 180°C/Fan 160°C/Gas 4.
Stir the rice into the veg. Pour in the spiced stock. Season and cover. Bake for 25 mins till the stock has been absorbed.
While the biriyani bakes, roughly chop the cashews.
Fish the bay leaf, cinnamon stick and cloves out of the rice. Taste and add more salt and pepper if you think it needs it. Fork in the spinach to just wilt it. Spoon the roast cauli biryani onto plates and serve with generous sprinkles of the cashews.