Remove the tough stems from the kale and chop the leaves into bite-size pieces.
Place the kale in a large bowl and add a pinch of salt. Massage the kale with your hands for 2-3 minutes until it softens and becomes darker green.
Toast the walnuts in a dry skillet over medium heat for 3-5 minutes until fragrant, stirring occasionally. Remove from heat and let cool.
Core and thinly slice the apples, keeping the skin on. If preparing ahead, toss with lemon juice to prevent browning.
In a small bowl, whisk together olive oil, apple cider vinegar, honey, salt, and pepper. Add Dijon mustard if using.
Add the apple slices, toasted walnuts, and any optional ingredients (cranberries, cheese, red onion) to the bowl with the massaged kale.
Drizzle the dressing over the salad and toss gently until everything is evenly coated.
Let the salad rest for 5-10 minutes before serving to allow flavors to meld.
