Remove any tough outer leaves from the cabbages. Quarter the green cabbage, remove core, then finely shred using a sharp knife, mandoline, or food processor until you have about 4 cups packed shredded cabbage. Repeat with the red cabbage to yield about 1 cup. Peel and grate or julienne the carrots to make 1 cup. Thinly slice 1/4 cup red onion and roughly chop 2 tablespoons fresh parsley.

Combine shredded green cabbage, shredded red cabbage, carrots, red onion and chopped parsley in a large mixing bowl. Toss briefly to distribute evenly and set aside while you make the dressing so the flavors can begin to mingle.

Creamy Dressing

Make dressing

In a medium bowl, whisk together 1/2 cup mayonnaise and 1/4 cup sour cream until smooth. Add 2 tablespoons apple cider vinegar, 1 tablespoon granulated sugar, 1 teaspoon Dijon mustard, 1/2 teaspoon celery seed, 3/4 teaspoon kosher salt, 1/2 teaspoon freshly ground black pepper and 1 teaspoon lemon juice (if using). Whisk thoroughly until sugar dissolves and dressing is silky and slightly thick.

Taste the dressing and adjust seasoning: add a little more vinegar for tang, more sugar for sweetness, or more salt/pepper as needed.

Combine dressing with cabbage

Pour the dressing over the prepared cabbage mixture. Using two large spoons or salad tongs, toss everything together until all vegetables are evenly coated. Toss gently but thoroughly so dressing clings to the shredded vegetables without crushing them.

For best texture and flavor, cover the bowl and refrigerate for at least 30 minutes to 2 hours to let the flavors meld and the cabbage soften slightly. If the slaw becomes too dry after chilling, stir in an additional 1–2 tablespoons mayonnaise or a splash of apple cider vinegar to adjust consistency and brightness.

Just before serving, give the coleslaw a final toss, taste and adjust salt/pepper if necessary. Serve chilled or at cool room temperature.