Step 1

Preheat your oven to 400F / 200C degrees. Scrub the potatoes, prick them all over with a fork, and sprinkle generously with sea salt. Bake the potatoes until tender throughout. This can take an hour for large potatoes. Less for smaller spuds.

Step 2

While the potatoes are baking, make the dressing. Whisk the vinegar, mustard, egg yolk, and olive oil with a big pinch of salt. Then whisk in the cheese, and finally the lemon juice. Taste, make any adjustments, and set aside.

Step 3

Slice a big cross into the top of each potato, then gently but firmly push in on the ends of each potato. This way the tops open up, and you can begin to spoon out a bit of the potato filling. Add a pat of butter/olive oil to each potato, or a splash of the dressing and a bit of salt. Toss the arugula with a generous amount of the dressing, and then pile it into the potatoes. You'll likely have some leftover dressing to enjoy as needed with the salad and skins.