Marinated Beets with Potatoes and Horseradish

Preheat oven to 400°. Wrap beets in foil and roast directly on a rack until tender, about 1 hour. Let cool, peel, and cut into 3/4” pieces. Place in a small bowl and toss with 2 tablespoons oil and 1 tablespoon vinegar; season with salt and pepper. Let sit at room temperature for 30 minutes. Meanwhile, toss the potatoes on a large rimmed baking sheet with 1 tablespoon oil and season with salt and pepper. Roast, tossing occasionally, until golden brown and tender, 25-30 minutes. Let cool slightly. Transfer potatoes to a large bowl and add scallions, mustard greens, dill, parsley, horseradish, lemon juice, remaining 4 tablespoons olive oil and remaining 1 tablespoon vinegar. Toss to combine; season with salt and pepper. Add beets and toss again. Serve drizzled with crème fraîche.