In a large bowl, toss the onion with the lemon juice and a pinch of salt. Let marinate for at least 10 minutes.
Remove the tough outer layer of the fennel bulbs. Using a mandoline or a sharp knife, thinly slice the bulbs crosswise.
Add the fennel, cabbage, carrot, parsley, and dill to the bowl of marinated onion. Sprinkle with 1 teaspoon salt and lightly massage the mixture with your hands for about a minute to wilt the cabbage a bit. Let the slaw rest for 15 minutes, discarding any liquid that collects in the bowl.
In a small bowl, whisk together the horseradish and vinegar, then whisk in the olive oil. Toss the slaw with the vinaigrette and the mayonnaise and serve.
Nutrition Facts
Amount Per Serving
Calories 206Calories from Fat 153
% Daily Value*
Fat 17g26%
Saturated Fat 2g13%
Trans Fat 1g
Polyunsaturated Fat 4g
Monounsaturated Fat 10g
Cholesterol 3mg1%
Sodium 102mg4%
Potassium 480mg14%
Carbohydrates 12g4%
Fiber 4g17%
Sugar 4g4%
Protein 2g4%
Vitamin A 2650IU53%
Vitamin C 50mg61%
Calcium 70mg7%
Iron 1mg6%
* Percent Daily Values are based on a 2000 calorie diet.