Add the broccoli slaw, chopped kale, and julienned apples to a mixing bowl. Toss together.
In a small bowl, combine the mayonnaise, mustard, vinegar, and celery seeds. Stir to combine. Season to taste with salt and pepper.
Pour the dressing over the slaw and toss to combine.
Notes
Slicing the apple: Cut the apple into matchstick-like strips. Leaving the skin on the apple will provide color and texture. If desired, remove the peel.Dressing: This slaw is not heavily dressed. For a creamier, more saucy slaw, double the amount of dressing.Storage: Store refrigerated for up to 3-4 days.