In a large pot, add potatoes with enough cold water to cover them. Bring to a boil and reduce to a simmer. Covered and cook for 20-30 minutes until the potatoes are fork tender. Drain.
Mash the potatoes until they begin to break down. Add in the buttermilk and herbs and continue to mash just until it reaches the desired consistency. Stir in the sour cream and butter and season with salt and pepper, to taste. Serve warm with extra butter. Serves 6.