When I make a vegetable biryani it seems rather stodgy and lacks flavour. Has chef any suggestions?

Victoria Blackmore, Settle

Vegetable biryani is a great vegetarian dish, but also I've found it a very suitable dish to give children a taste of Indian food - flavoursome but not overly hot. Break 1 cauliflower into florets, peel and dice 1 large potato and 1 orange sweet potato, peel and finely dice 1 large onion. Put 2 tbsp vegetable oil into a large roasted tray, add the chopped vegetables and mix around, roast in an hot oven for about 15 minutes. Add 2 tsp ginger paste, half a tsp ground nutmeg, half tsp ground mace, 2 tsp chilli powder, 2 small cinnamon sticks, and 10 white cardamom pods to the vegetables and cook for further 5 minutes. Add 450g of rinsed and drained basmati rice, then add 1 litre of hot vegetable stock. Dice some green beans and add to the rice, then sprinkle a few saffron strands over the top. Season with salt and pepper. Cover with foil and bake for about 30 minutes or until the liquid has evaporated. Garnish with some freshly chopped coriander, a few lemon wedges and some chopped roasted cashew nuts.