Roasted Beet Toasts with Horseradish Cream

medium red and yellow beets, about 1 1/2 inches wide

Olive oil, for rubbing

Salt and freshly ground black pepper

slices of cocktail rye bread or sixteen 3-inch squares or rounds of thinly sliced dense rye bread

unsalted butter, melted

crème fraîche

heavy cream

prepared horseradish, drained

chopped parsley

red wine vinegar

red pearl onions, peeled and thinly sliced

Chervil sprigs and minced chives, for garnish