1. Preheat the oven to 180C.
2. Microwave the jackets, pricked with metal skewers, for 5 minutes to get them going, or else they take ages in the oven.
3. Bake them for about an hour. As long as they are cooked through, they're good - it depends on how large they are.
4. Fry the sliced spring onion in a little oil over a low heat to soften, for about 5 minutes.
5. Meanwhile, mix the mayo, dijon, basil - add the spring onions when ready. When the jackets are ready, slice them in two, and carefully scoop out the potato. Mash roughly with the other ingredients.
6. Place the filling back into the shells. Bake for 15-20 minutes or until brown and bubbling.
7. Serve with some salad or as a side for sausages.