Preheat the oven to 180 degrees C fan.
Clean the potatoes & cut off any bad spots, but don’t peel them.
Cut the potatoes bite-sized pieces.
Add olive oil & salt & pepper & mix well - all potato pieces should be covered w/ olive oil.
Line a deep baking tray w/ baking parchment.
Add the rosemary.
Add the potatoes.
Bake in the preheated oven for 30 min.
Let the potatoes cool for about 10 min.
Discard the rosemary.
While the potatoes are in the oven: chop spring onions & cornichons.
Mix both w/ olive oil & balsamic vinegar.
If the potatoes have done their 10 min rest mix hot potatoes & the spring onion-cornichon mix & let it cool completely.
In the meantime boil the eggs until very well done.
Peel them & cut them w/ help of an egg slicer (use the egg slicer twice for each egg!).
Add mayonnaise & sour cream & mix well.
Add salt & pepper.
Add thyme & chives - save some chives for decoration.
Store the dressing in the fridge.
If the potato mix is at room temperature add the dressing & mix well.
Optional: use chopped chives & tomatoes for decoration.