Sweet potato jackets with gruyere and black beans

Preheat the oven to 200ºC, gas mark 6. Prick the sweet potatoes all over with a fork and put on a baking tray. Roast for 50 minutes-1 hour, until tender to the core.

Meanwhile, heat the oil in a pan over a medium heat. Add the onion and garlic; sauté for 8 minutes until softened, taking care not to let them burn. Add the spices and cook for another 3 minutes until aromatic, then add the black beans, tomatoes and 150ml water. Bring to the boil, then simmer until almost all the liquid has evaporated; season.

With a knife, split open the tops of the sweet potatoes. Divide the butter between them and top with the black bean mixture and gruyère. Bake for 5 minutes until the cheese has melted. Top with the crème fraîche (or Greek yogurt), coriander, chilli flakes, some freshly ground black pepper and a little drizzle of olive oil.