Prepare. Start by preparing the ingredients as indicated above. This includes toasting your walnuts, shredding the sprouts, slicing the celery, grating the carrots, and slicing the apple
Toss. Add your prepared ingredients, except for the walnuts, to a large bowl and toss the ingredients a few times to combine.
Dressing. To make the dressing, in a smaller bowl, whisk together the mustard, maple syrup, olive oil and apple cider vinegar. You can add seasonings as desired.
Finish. Pour half of dressing over the ingredients in the large bowl and then toss. Add the remaining dressing, or as much as desired, and toss again.
Serve. Gently toss in the walnuts and serve.