Save half of the potatoes for Sunday's steak hash.
1. Preheat oven to 425°.
2. Place potatoes on a baking sheet. Drizzle potatoes with 1 tablespoon oil; sprinkle with salt and 1/4 teaspoon pepper. Toss to coat. Bake at 425° for 30 minutes or until golden brown. Cool potatoes slightly.
3. Place the remaining 1 tablespoon oil, 1/4 teaspoon pepper, and mustard in a large bowl; stir well with a whisk. Add half of roasted potatoes and parsley; toss gently to coat. (Reserve remaining potatoes for Sunday brunch.) Serve at room temperature.