½ small green cabbage (about 1 pound), cored and coarsely chopped
⅛ small red cabbage (about ¼ pound), cored and coarsely chopped
2 teaspoons kosher salt, plus more as needed
½ cup coarsely grated carrot
1 cup thinly sliced green bell pepper
½ cup thinly sliced red onion
¾ cup vegan mayonnaise
2 tablespoons unseasoned rice vinegar
2 tablespoons apple cider vinegar
2 teaspoons raw cane sugar
¼ teaspoon molasses
¼ teaspoon whole-grain mustard
⅓ teaspoon celery seeds
Freshly ground white pepper
Combine the cabbages and 2 teaspoons of the salt in a large bowl. With clean hands, massage the cabbage until soft and wilted, about 3 minutes. Transfer to a colander set in the sink and rinse the bowl. Put a plate atop the cabbage and weight it down (a 28-ounce can of tomatoes works well for this). Let sit for 1 hour.
Rinse the cabbage under cold water, then transfer it back to the bowl. Add the carrot, bell pepper, and onion. With clean hands, mix well.
In a small bowl, whisk together the mayonnaise, vinegars, sugar, molasses, and mustard. Pour just enough of the dressing into the bowl to moisten the slaw and mix well with clean hands. Add the celery seeds, taste, and season with salt and pepper. Cover and refrigerate for at least 1 hour.
Bring to room temperature and toss well before serving, adding a tad bit more dressing, if desired.