Wash the potatoes, but don’t peel them. 

Put them into a medium pot and cover with water by 2 inches (5 cm) or so. 

Add a pinch of kosher salt to the pot and bring to a boil.

Reduce to a roiling simmer, then cook until the potatoes are fork tender (but not mushy), about 10-15 minutes. 

Meanwhile, in a medium pot, add the broth, vinegar, mustard, sugar, salt, and pepper. 

Bring to a boil, wait 10 seconds, then take off the heat. 

Transfer to a large bowl, add the onions and set aside. 

Drain the potatoes, dump them onto a cutting board, then let them cool until they’re easy to handle. 

Use a butterknife or your fingers to peel the potatoes. 

Slice them into 1/4 inch (0.5 cm) slices then transfer the slices to the beef broth mixture. 

Add the chopped herbs to the bowl and gently toss everything, so the potato slices get completely covered by the sauce. 

There sauce should be very soupy and plentiful. This is okay, since you will serve the potatoes with a slotted spoon, leaving the majority of the sauce behind. 

Let the potatoes sit in the marinade for at least 1 hour. If they are all submerged under the liquid, you could even marinate them in the fridge over night. The longer they sit, the more flavourful they will be. 

Serve the potatoes with a slotted spoon, leaving the majority of the liquid behind. Enjoy!