Smoked Fish, Watercress & Apple Salad & Horseradish dressing

1 cup whipping cream
1/3 cup prepared horseradish
4 tablespoons olive oil
2 tablespoons apple cider vinegar
2 teaspoons apple cider vinegar
2 teaspoons freshly chopped dill
1/8 teaspoon cayenne
6 cups trimmed watercress sprigs (2 bunches)
1/2 cup very thinly sliced red onion
2 red apples, cored and thinly sliced
9 ounces smoked fish
fresh dill sprigs
Whisk cream, horseradish, 2 tablespoons oil, 2 tablespoons vinegar, chopped dill and cayenne in a small bowl to blend. Season to taste with salt and pepper. Place watercress in a large bowl. Add 1/3 cup cream dressing, 2 tablespoons oil and 2 teaspoons vinegar and toss to coat. Season to taste with salt and pepper. Mound watercress in center of each of 6 plates. Top with sliced onion. Fan apple slices atop each salad, then top with smoke fish.
Spoon dressing over each salad and garnish with dill sprigs.