Mustard-Roasted Potatoes & Turnips

via Smitten Kitchen.
Makes 10 servings

Nonstick vegetable oil spray
1/2 cup whole grain Dijon mustard
2 tablespoons extra-virgin olive oil
2 tablespoons (1/4 stick or 1/2 ounce) butter, melted
2 tablespoons fresh lemon juice
3 garlic cloves, minced
1 tablespoon dried oregano
1 teaspoon finely grated lemon peel
1 teaspoon coarse kosher salt
3 pounds 1- to 1 1/2-inch-diameter mixed unpeeled red-skinned and white-skinned potatoes or turnips, cut into 3/4-inch-wide wedges

Position 1 rack in top third of oven and 1 rack in bottom third of oven and preheat to 425°F. Spray 2 large rimmed baking sheets with nonstick spray. Whisk mustard, olive oil, butter, lemon juice, garlic, oregano, lemon peel, and salt in large bowl to blend. Add potatoes or turnips; sprinkle generously with freshly ground black pepper and toss to coat. Divide between prepared baking sheets, leaving any excess mustard mixture behind in bowl. Spread potatoes/turnips in single layer. Roast 20 minutes. Reverse baking sheets and roast until they are crusty outside and tender inside, turning occasionally, about 25 minutes longer.
Transfer to serving bowl.
Do ahead: Can be made 2 hours ahead. Let stand on baking sheets at room temperature. Rewarm in 425°F oven 10 minutes.