- 2 pounds yellow-fleshed potatoes such as Yukon Gold
- 1 1/4 lb turnips
- 2 1/4 teaspoons salt
- 7 tablespoons unsalted butter, cut into tablespoons
- 1 cup coarse fresh bread crumbs (from 2 slices firm white sandwich bread)
- 2 tablespoons drained bottled horseradish, patted very dry between paper towels
- 3/4 cup whole milk
- 1/2 cup thinly sliced scallion greens
- Unsalted butter for buttering pan
- 1 teaspoon finely grated fresh orange zest
- 1 1/4 cups fresh orange juice
- 2 tablespoons molasses (not robust or blackstrap)
- 1/2 teaspoon salt
- 1/4 teaspoon black pepper
- 4 large sweet potatoes (2 3/4 lb), peeled and cut lengthwise into 1-inch-wide wedges
- Peel potatoes and turnips, then cut into 2-inch pieces. Cover potatoes, turnips, and 2 teaspoons salt by 2 inches cold water in a 6-quart pot. Bring to a boil, then reduce heat and simmer, uncovered, until potatoes are tender, 15 to 18 minutes.
- While vegetables cook, melt 3 tablespoons butter in a 10-inch heavy skillet (preferably cast-iron), then toast bread crumbs with remaining 1/4 teaspoon salt, stirring frequently, until golden brown, 3 to 5 minutes. Add horseradish and toss until combined well, then transfer to a small bowl.
- Drain vegetables in a colander, then return to pot and mash. Stir in milk, remaining 4 tablespoons butter, and scallion greens over low heat until combined well and heated through. Season with salt and pepper, then serve topped with bread crumbs.