Remove and discard the thick stems from the kale. Chop or tear the leaves into smaller pieces. Rinse the kale well under cool running water, then dry it thoroughly in a salad spinner or with a clean kitchen towel.
Chop the Granny Smith apple into bite-sized pieces. For extra protection against browning, place the apple in a small bowl, squeeze the lemon juice over it, and toss to coat. This step is optional, but recommended for meal prepping.
Add the apple cider vinegar, Dijon mustard, minced garlic, salt, and freshly cracked pepper to a bowl. Whisk until combined. Slowly stream in the olive oil, whisking constantly, until the vinaigrette is smooth and emulsified. Alternatively, blend all the dressing ingredients together until smooth. Taste and adjust the salt and pepper as needed.
Add the kale to a large bowl and pour half of the Dijon vinaigrette over top. Using clean hands, gently massage the dressing into the kale for 1-3 minutes, or until the leaves look darker and glossier and feel noticeably softer.
Add the walnuts, prepared apple, and raisins to the kale, then toss until evenly combined.
Taste the salad and add more vinaigrette as desired (I used the whole batch). Serve immediately or refrigerate until ready to eat.
*I used curly kale in this recipe as it’s affordable and easy to find, but dinosaur (lacinato) kale works just as well. You can also use pre-chopped bagged kale to save a little prep time (use ½ lb.)**The lemon juice is optional, but it keeps the apples bright and prevents them from browning. It also helps keep the kale bright green and assists with the overall fresh flavor of the dressing. You can discard the leftover lemon juice after you’ve tossed the diced apples, or just add it to the bowl if you like a little more tang in your salad dressing! (I do.)Storage: Store leftovers in an airtight container in the refrigerator for up to 3-4 days. I don't recommend freezing this salad because the apples lose their texture after thawing, and the dressing and kale become watery and limp.