Ingredients

• 4 pounds large boiling potatoes (preferably white-fleshed)
• 3/4 stick unsalted butter, cut into pieces
• 1 1/4 cups whole milk
• 3 large egg yolks
• Nigella seeds (sometimes mislabeled "black onion seeds") or caraway seeds for garnish
• Equipment: a potato ricer or a food mill fitted with medium disk; a pastry bag with 3/4-inch plain tip

Instructions

1. Peel and quarter potatoes, then cover with water in a 4-quart pot and season well with salt. Simmer, partially covered, until tender, 15 to 20 minutes.
2. While potatoes are simmering, heat butter and milk in a small saucepan until butter is melted. Remove from heat and cover to keep warm.
3. Preheat oven to 400°F with rack in middle.
4. Drain potatoes and force through ricer into a large bowl (or mixer bowl if using stand mixer). Beat in milk mixture, yolks, and 1/2 teaspoon each of salt and pepper with an electric mixer at low speed until combined.
5. Spread about one-third of potatoes in a buttered 1 1/2-quart shallow ovenproof dish. Transfer remaining potatoes to pastry bag. Pipe potatoes close together into 2 1/2- to 3-inch-high pointed mounds to form "'ghosts" and garnish each mound with 2 seeds for "eyes."
6. Bake until tips of ghosts are golden and potatoes are firm, 20 to 25 minutes.