Marinated Beets with Potatoes and Horseradish

Name: Marinated Beets with Potatoes and Horseradish
Ingredients: 3 medium beets (about 1 pound); 7 tablespoons olive oil, divided; 2 tablespoons Sherry vinegar or red wine vinegar, divided; Kosher salt, freshly ground pepper; 1 pound waxy potatoes (such as Yukon Gold), cut into 1-inch pieces; 3 scallions, thinly sliced; 1 cup coarsely chopped mustard greens; ¼ cup chopped fresh dill; 2 tablespoons chopped fresh parsley; 2 tablespoons freshly grated horseradish or 1 prepared horseradish; 1 tablespoon fresh lemon juice; ⅓ cup crème fraîche