Preheat the oven to 200°C, fan 180°C, gas 4. Prick the potatoes all over with a fork. Place directly on the top rack in the oven and bake for 1 hour.
About 5 minutes before the end of cooking time, tip the beans into a pan and warm through.
Cut open the potatoes and spread each with a little butter. Spoon over the beans, top with grated Cheddar and serve.