Ingredients

• 3 medium beets (about 1 1/2 pound with greens)
• 1/4 cup finely chopped shallots
• 2 tablespoons white-wine vinegar
• 2 1/2 tablespoons fresh lemon juice, or to taste
• 1/4 teaspoon sugar
• 1/4 cup extra-virgin olive oil
• 1/2 pound sliced smoked sablefish (black cod), chopped (about 1 1/3 cups)
• 2 bunches watercress, torn into small sprigs (6 cups)
• Equipment: heavy-duty foil; a 2 1/2-inch pastry ring or cookie cutter without a handle

Instructions

1. Preheat oven to 450°F with rack in middle.
2. Trim beets, discarding stems and greens (or reserve for another use), then wrap together in foil and roast until tender, about 1 1/4 hours. Let beets stand in foil at least 15 minutes, then remove from foil and cool. Remove skins and cut beets into 1/3-inch dice.
3. Whisk together shallots, vinegar, lemon juice, sugar, 1/2 teaspoon salt, and 1/4 teaspoon pepper, then whisk in oil. Reserve 2 tablespoon vinaigrette for watercress and toss remainder with beets. Let marinate at room temperature 30 minutes.
4. To serve: Drain beets in a sieve set over a bowl and set beet vinaigrette aside. Put pastry ring in center of a salad plate and gently press about 2 1/2 tablespoons fish into bottom of ring, then put about 1/4 cup beets over fish. Repeat on 7 more plates. Toss watercress with reserved 2 tablespoons vinaigrette and mound over beets (a small handful per plate). Drizzle a little beet vinaigrette around each plate.
5. Drain beets in a sieve set over a bowl and set beet vinaigrette aside.
6. Put pastry ring in center of a salad plate and gently press about 2 1/2 tablespoons fish into bottom of ring, then put about 1/4 cup beets over fish. Repeat on 7 more plates.
7. Toss watercress with reserved 2 tablespoons vinaigrette and mound over beets (a small handful per plate). Drizzle a little beet vinaigrette around each plate.