1. Preheat the oven to 220°C/Gas Mark 7.
2. Set the potatoes directly on the rack in the centre of the oven and bake until easily pierced with a fork, about 1 hour. Remove from the oven and turn the heat down to 200C/Gas Mark 6.
3. Cut a slit in the top of the potatoes and carefully scoop out the flesh into a bowl, leaving the shells intact. Mash the potato lightly with a fork. Add the butter, sour cream, and 35g of the cheese, any toppings and salt and pepper to taste. Refill the shells with the potato mixture mounding it slightly.
4. Set the potatoes on a baking sheet, and bake until heated through, about 15 to 20 minutes. Sprinkle the tops with the remaining cheese and bake until melted, about 5 minutes. Serve immediately.