Bring 1 inch of water to a boil in a large saucepan fitted with a steamer basket. Add beets, cover and cook until tender, 10 to 12 minutes. Combine 2 tablespoons vinegar, 1 tablespoon syrup and a pinch of salt in a bowl. Stir in the beets. Refrigerate for at least 10 minutes and up to 2 days.
To serve, whisk the remaining 2 tablespoons vinegar, 2 teaspoons syrup, 1/4 teaspoon salt, oil and pepper in a large bowl. Add watercress and sliced fennel; toss to coat. Arrange the beets around the edge of a platter and drizzle with 2 tablespoons of the pickling liquid. Mound the salad in the center. Top with pistachios and cheese. Garnish with chopped fennel fronds, if desired.
1 pound medium beets, peeled and sliced into 1/4-inch rounds
4 tablespoons champagne vinegar or white-wine vinegar, divided
1 tablespoon pure maple syrup plus 2 teaspoons, divided
Pinch of salt plus 1/4 teaspoon, divided
3 tablespoons extra-virgin olive oil
¼ teaspoon ground pepper
10 cups watercress, trimmed
1 medium fennel bulb, trimmed, cored and thinly sliced; fronds reserved
¼ cup coarsely chopped salted pistachios
¼ cup crumbled feta or goat cheese or vegan substitute