Place the potatoes in a large pot, cover with 4 inches of cold water, and add 2 tsp of sea salt. Bring to a boil, turn down the heat, and simmer for 15 minutes or until the potatoes are tender when pierced. Reserve a cup of cooking water and strain the potatoes.
With the back of a spoon, gently smash the potatoes and return them back to the pot with the butter and 1/2 tsp sea salt. Gently stir to coat. Start adding a few spoonfuls of potato water at a time, stirring and creating a butter sauce that will coat the potatoes. Taste for seasoning. Add the parsley and any extra potato water if needed. Place the potatoes in a large serving bowl. Top with dollops of creme fraiche, chives, and freshly ground black pepper.