Toss cabbage and 1 teaspoon salt in colander or large mesh strainer set over medium bowl. Let stand until cabbage wilts, at least 1 hour or up to 4 hours. Rinse cabbage under cold running water (or in large bowl of ice water if serving slaw immediately). Press, but do not squeeze, to drain; pat dry with paper towels. (Can be stored in sealable bag and refrigerated overnight.)
Stir together onion, honey, vinegar, oil, mustard and tarragon in medium bowl; set dressing aside. Immediately toss cabbage, apple and fennel in dressing. Season, to taste, with salt and pepper; cover and refrigerate until ready to serve.
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