Thinly slice the red cabbage using a sharp knife or mandoline slicer. Aim for slices no thicker than 1/8 inch. Place in a large mixing bowl.
Add the freshly grated carrot to the bowl with the cabbage.
Thinly slice the red onion and add to the bowl. If you find raw onion too strong, you can soak the slices in cold water for 10 minutes before adding.
If using optional add-ins like apple, parsley, sunflower seeds, or cranberries, add them to the vegetable mixture and toss to combine.
In a small separate bowl, whisk together the apple cider vinegar, olive oil, honey, Dijon mustard (if using), caraway seeds (if using), salt, and pepper until well combined.
Pour the dressing over the vegetable mixture and toss thoroughly to ensure everything is well coated. Use clean hands or tongs to massage the dressing into the cabbage slightly.
Let the salad rest for at least 10 minutes before serving to allow the cabbage to soften slightly and the flavors to meld together.
Just before serving, give the salad another good toss and taste for seasoning, adding more salt and pepper if needed.
