Pour the coleslaw mix into a strainer and place in the sink. Sprinkle with ½ cup of the sugar and ¼ cup of the kosher salt and lightly toss. Let sit for 5 minutes to draw out the moisture from the cabbage and then rinse well with cold water. Spin the coleslaw mix in a salad spinner and place in a large bowl.*
For the dressing, in a medium bowl mix the mayonnaise, 2 tablespoons sugar, cinder vinegar, celery salt, 1 teaspoon kosher salt, freshly ground black pepper, chopped onions and chopped parsley. Whisk well and pour ⅔ of the dressing over the cabbage mixture, and toss to combine. Add more of the dressing as desired and season with more salt, pepper or parsley to taste.
Refrigerate for 30 minutes up to overnight and serve.
Notes
*You can also dry the coleslaw mix by spreading it onto a paper towel-lined baking tray and blotting it dry with more paper towels. Or you can roll the wet cabbage mix in a clean tea towel and then gently squeeze it to soak up the extra moisture.