Preheat the oven to 180 degrees Celsius or 356 degrees Fahrenheit.
Wash the potatoes and cut into reasonably large bite sized pieces.
Pour the water and oil into your large baking dish. Add the lemon juice, oregano, Maille Dijon mustard and seasoning. Stir to combine. Arrange some rosemary sprigs in the bottom of the dish, reserving a few to thread between the potatoes. Add the lemon rinds, a couple at either end of the dish. Finally, arrange the potatoes, and stir them around a little with your hands to coat them in the flavours.
Cook the potatoes for 30 minutes. Once the 30 minutes is up, generously toss the potatoes in the dish to submerge any parts that are becoming crispy. Return to the oven for another 30 minutes.
While the potatoes are cooking, mix together the ingredients for the mustard mayonnaise dressing. Taste and adjust for seasoning and your personal preference.
Toast the pine nuts gently in a dry pan, and finely chop radicchio and herbs. Finely chopping the dill is particularly important, as long strands of dill in a potato salad can be annoying to eat.
Once the potatoes have cooked for an hour, remove them from the oven. After allowing to cool for a few minutes, remove them from the baking dish, leaving any liquid, rosemary or lemon rind behind. Transfer them to a large mixing bowl. You can use this tray of leftover flavourings to lightly roast cabbage or capsicum as an accompaniment to the meal.
Add the mustard mayonnaise dressing to the salad, and gently mix to combine. Add 3/4 of the olives, pine nuts, herbs and radicchio, and continue mixing until everything is incorporated and covered in dressing. Plate the potato salad, and add the remaining ingredients. Not only do some fresh ingredients look pretty, but they add a textural element as they’re not coated in dressing. Serve warm or cold.