In a small bowl, whisk together the sour cream, vinegar, sugar, onion powder, garlic powder, celery salt, and pepper until smooth and well combined. This creates an emulsified dressing that will coat the cabbage evenly. I prefer to make the dressing first so all the seasonings fully dissolve and bloom in the sour cream, which gives you a more cohesive flavor rather than crunchy seasoning bits in the finished coleslaw.

Place the coleslaw mix in a large bowl and pour the dressing from Step 1 over it. Toss well, making sure every strand of cabbage gets coated with the creamy dressing. Fold in the fresh parsley, which adds brightness and a bit of color. The cabbage will start releasing its own liquid, which mixes with the dressing to create a nice, silky consistency.

Cover the bowl and refrigerate for at least 30 minutes, though up to 4 hours is ideal. This chilling time allows the cabbage to soften slightly while staying crisp, and the flavors meld together beautifully. Before serving, give it a good stir to redistribute the dressing, as the cabbage continues to release moisture. I find that coleslaw actually tastes better after sitting for a couple hours—the flavors deepen and the texture becomes more tender without getting mushy.