SALT CABBAGE Toss cabbage, carrot, onion, and salt in colander set over bowl. Let stand until wilted, about 1 hour. Rinse cabbage mixture under cold water, drain, and dry well with kitchen towel.
DRESS SLAW Whisk mayonnaise, sour cream, vinegar, sugar, and pepper in large bowl. Stir in cabbage mixture and refrigerate until chilled, at least 30 minutes. Serve. (Coleslaw can be refrigerated in airtight container for 2 days.)
