Smoked trout and a creamy horseradish dressing stand in for the classic tuna and vinaigrette in this composed salad. Rather than serving the dressing on the side, you could dress the vegetables separately before arranging them on plates.
Preheat the oven to 425°. Wrap the beets in foil and bake for about 1 hour, or until tender when pierced. When cool enough to handle, peel the beets and cut them into 2-by- 1/2 -inch matchsticks or small wedges.
Bring a medium saucepan of lightly salted water to a boil. Add the haricots verts and cook until tender, about 4 minutes. Using a slotted spoon, transfer the beans to a colander and rinse under cool running water; pat dry. Pour off all but 2 inches of water from the pan and set a steamer basket inside. Add the potatoes and steam until tender, about 18 minutes. Let cool slightly, then quarter the potatoes.
In a medium bowl, combine the shallots, horseradish, vinegar, sour cream and mustard. Whisk in the oil, 1 tablespoon at a time, until emulsified. Whisk in the heavy cream and season with salt and pepper.
Just before serving, stir the dill into the dressing. In a bowl, toss the flaked trout with 1/4 cup of the dressing and mound on 4 large dinner plates. Garnish each serving with the beets, haricots verts, potatoes, eggs and tomatoes. Pass the remaining dressing separately.
Make Ahead: The vegetables and dressing can be refrigerated overnight.