- Position a rack in the center of the oven and preheat to 350 degrees. Butter a 2½-quart baking dish.
- Pierce potatoes in several places with a fork and arrange them in a single layer on oven rack with a sheet of foil on rack below to catch any drips. Roast until tender, about 40 minutes.
- When cool enough to handle, peel potatoes and force them through a food mill into a large bowl, or mash them with a potato masher until smooth.
- While the potatoes are still warm, add the brown sugar, preserves, sherry, melted butter, lemon zest, lemon juice, nutmeg, cinnamon, ginger, and salt, and beat with a wooden spoon until well-mixed.
- Scrape potato mixture into prepared dish, smooth top, and bake until heated through, about 20 minutes. Serve warm.