Preheat oven to 425°F. Cut potatoes in half lengthwise; cut each half lengthwise into 3 wedges (about 1-inch-thick). Toss potato wedges with salt and 2 tablespoons of the oil on a large rimmed baking sheet.
Bake in preheated oven until potatoes are deep golden brown, 35 to 40 minutes, stirring twice with a metal spatula during baking to brown on all sides. Remove from oven and cool 20 minutes.
Whisk together vinegar, pepper, mustard, and remaining 1/4 cup oil in a medium bowl until well blended; whisk in cheeses. Add potatoes, and toss to coat. Sprinkle with parsely, if desired, and serve immediately.