Heat your oven to 220°C/Fan 200°C/Gas 8. Tip the rice into a bowl. Cover with cold water. Whisk (you can use a fork) for 1-2 mins till the water turns cloudy (this is the starch). Drain the rice and tip back into the bowl. Cover with more cold water. Set aside.
Add 1 tbsp olive oil to a shallow ovenproof casserole dish or roasting tin. Slide into the oven to heat. Take the leaves off the cauliflower and break it into small florets, chopping any stems into bite-size pieces. Trim and finely slice the leek.
Add the cauliflower and leek to the casserole dish. Add the chicken. Toss to coat in the oil. Season with a little salt and pepper. Roast in the oven for 20 mins.
While the veg and chicken roast, peel and grate the ginger. Finely chop the chilli, flicking out the seeds and white bits for less heat. Crumble the stock cube into a heatproof jug. Add the chilli and ginger.
Add 2 tsp of curry powder to the jug. Stir in 450 ml boiling water. Turn the oven down to 180°C/Fan 160°C/Gas 4.
Drain the rice. Take the dish out of the oven. Stir in the rice. Pour in the spiced vegetable stock. Add 1 bay leaf. Season with a little salt and pepper. Cover with a lid (or use foil if you don’t have a lid). Bake in the oven for 25 mins till the stock is absorbed.
While the biryani cooks, warm a dry frying pan over a medium heat. Add the cashews. Toast for 2-3 mins till golden brown. Tip out of the pan and let them cool a little, then roughly chop.
Fish the bay leaf 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. Serve the rice in warm bowls topped with the chopped cashews and a spoonful of yogurt.