How to Make It
Preheat the oven to 350°. Put the beets in a small roasting pan and add 1/2 cup of water. Cover the pan with foil and bake the beets for 1 hour, until tender. Let cool slightly, then peel and slice them 1/8 inch thick. Drizzle with a little oil and season with salt and pepper.
Meanwhile, brush the rye bread with the melted butter and arrange on a baking sheet. Bake for about 8 minutes, until crisp.
In a small bowl, whisk the crème fraîche and cream until thick. Fold in the horseradish and parsley; season with salt and pepper.
In a small saucepan, bring the vinegar and 1/4 cup of water to a boil. Add the pearl onions and simmer over moderate heat for 1 minute. Season the onions with salt and let cool in the brine. Drain the onions on paper towels.
Arrange the beet slices on the toasts, overlapping them slightly. Scatter the pickled onions over the beets. Top with small dollops of the horseradish cream, garnish with chervil sprigs and chives and serve.