Boil the potatoes in a large pot of salted water until they are tender, about 10 to 15 minutes.
Drain the potatoes and let them steam under a kitchen towel for 15 to 20 minutes.
In a separate bowl, create the dressing by whisking together mayonnaise, buttermilk, mustards, dill, and some of the seasoning.
Peel the cooled potatoes and cut them into bite-sized pieces before adding them to a large mixing bowl.