Preheat the oven to 220C/gas mark 7. Peel 850g of sweet potatoes, cut them into large pieces, then pile them into a steamer basket or colander resting over a pan of boiling water. Cover tightly with a lid and let them steam for about 15 minutes, maybe less, until they are tender enough to crush. Put 500g of tomatoes in a baking dish and trickle them with 4 tbsp of olive oil. Peel and finely slice 2 medium-sized cloves of garlic and add them to the tomatoes. Chop 6 spring onions and add them, stirring them into the oil. Stir in 2 tsp of mustard seeds and 1 level tsp of turmeric. Season with sea salt. Toss the tomatoes, aromatics and oil together. Bake for 25 minutes or until the tomato skins have browned. When the sweet potatoes are completely soft and tender, remove from the pan and crush them with a fork or potato masher, then pile on to 2 plates. Lightly crush the cooked tomatoes with a fork, pressing down on them until their juices escape, then spoon everything over the sweet potatoes. Serves 2 The sugary flesh of sweet potato responds well to sweet-sour tomatoes, roasted till soft and crushed. Vegan as it stands, you could add chorizo or pancetta to the tomatoes if you wish. Cut a cooking chorizo into small pieces and add to the tomatoes as they go in the oven. If you prefer, you could bake the sweet potatoes for 45 minutes until tender, then split them open and spoon over the tomatoes and their juices. If the potatoes have firm skins, you could slice the cooked potato in half, scrape out the flesh and mash it with a fork, then stir in the crushed roast tomatoes and pile back into the skins.