In a small bowl, whisk together the fresh lemon juice, Dijon mustard, sweetener, and olive oil. Set the dressing aside.

Working with one apple at a time, cut each apple into quarters. Remove the peel and seeds, then cut each quarter in half crosswise and slice into thin wedges.

Toss the apple slices with a small amount of the dressing as soon as they are cut to help prevent them from browning.

Toast the walnuts in a dry skillet over medium-high heat for about 2 minutes, or until fragrant and lightly toasted. Transfer to a plate to cool.

Wash the celery stalks and dry them thoroughly. Separate the leaves from the stalks. Chop enough celery leaves to make about ½ cup.

Thinly slice the celery stalks, enough to make about 2–3 cups.

In a large bowl, combine the sliced celery, chopped celery leaves, and apples with their dressing. Toss gently to combine.

Add more dressing as needed, just enough to moisten the apples and celery without making the salad overly wet. You may not need all of the dressing.

Season with salt to taste.

Coarsely chop the toasted walnuts and add them to the salad along with the dried cranberries, if using. Gently toss to combine and serve.