In a small bowl, combine the mayonnaise, peppercorns and 1/4 teaspoon ground pepper. Cover and refrigerate until serving., Peel and cut sweet potato in half widthwise; cut each half into 1/2-in. strips. Place in a small bowl. Add 1 tablespoon oil, 1/4 teaspoon salt and 1/8 teaspoon pepper; toss to coat. Spread onto a parchment paper-lined baking sheet., Peel and cut beets in half; cut into 1/2-in. strips. Transfer to the same bowl; add the remaining oil, salt and pepper. Toss to coat. Spread onto another parchment paper-lined baking sheet., Bake vegetables, uncovered, at 425° for 20-30 minutes or until tender, turning once. Serve with peppercorn mayonnaise.