Toss the potatoes in a bowl with the oil, salt, and pepper until completely coated. Place on a baking sheet and bake until fork tender, about 45 minutes.
Meanwhile, bring a small pot of water to a boil and salt it generously. Fill a medium bowl with ice water. Put the chives in the boiling water and cook until bright green, about 30 seconds. Immediately, plunge into the ice water to set the color. Squeeze all the water out of the chives and give them a rough chop. Put into a blender with the sour cream. Pulse until you have a smooth green sauce and season with salt and pepper, to taste. Chill until ready to serve. (Or, thinly slice the chives and stir into the sour cream, season with salt and pepper, to taste.)
Cut the potatoes lengthwise and then across. Pinch and press the sides to open the potatoes. Divide the butter among the potatoes and serve with the sour cream. Garnish with crumbled bacon if desired.