1. 1. Preheat the oven to 400°F (200°C).

2. 2. Wash the baking potatoes and pierce them with a fork.

3. 3. Rub the potatoes with extra-virgin olive oil and sprinkle with salt.

4. 4. Bake the potatoes in the preheated oven for about 45-60 minutes, or until they are tender.

5. 5. Remove the potatoes from the oven and let them cool slightly.

6. 6. Cut the potatoes in half and scoop out the flesh into a bowl, leaving a thin shell.

7. 7. Mash the potato flesh with butter, gruyere cheese, cheddar, and ground mustard until well combined.

8. 8. Spoon the mixture back into the potato shells and top with additional cheese if desired.

9. 9. Place the stuffed potatoes back in the oven and bake for an additional 10-15 minutes, or until the cheese is melted and bubbly.

10. 10. Serve hot and enjoy!