Preheat oven to 400ºF.
Place the potatoes into a large pot with some salt and cover with cold water. Place the pot over medium-high heat and bring up to a bubble. Cook the potatoes until just tender but not fully cooked, about 12-15 minutes. Drain.
Scatter the potatoes onto a baking sheet and cover with another baking sheet. Lightly tap the second sheet pan with a skillet to crush the potatoes slightly. Remove the second sheet and toss the potatoes with the EVOO and some ground black pepper. Roast until crispy and deep golden brown, about 20 minutes.
While the potatoes are roasting, stir the mustard, sour cream, breadcrumbs and chives together in a mixing bowl. Season the dipper with salt and pepper.