Beet and Carrot Slaw

In a large bowl, whisk together orange juice, oil, vinegar, and mustard; season with salt and pepper. Cut greens off beets; discard stems and cut leaves into 1/4-inch-wide strips. Peel and grate beets; place in a strainer and rinse until water runs clear, then squeeze dry with a paper towel. Add to bowl along with beet leaves and carrots. Toss to combine. Let stand 15 minutes before serving.