For the Dressing:
- Halve and quarter the head of cabbage and cut out the core. Slice across into 1/2-inch ribbons. Place cabbage in a bowl and sprinkle in salt. Massage cabbage until it begins to soften, about 1 minute. Let rest for 10 minutes, tossing occasionally. Transfer cabbage to a colander and rinse well under cold water. Let drain thoroughly.
- Mix mayonnaise, Dijon mustard, grain mustard, honey, cayenne pepper, and vinegar together in a large bowl.
- Squeeze cabbage as dry as possible and add to the dressing. Mix until thoroughly combined. Cover top in plastic wrap and refrigerate at least 1 hour. Toss and taste before serving.