4 pounds boiling potatoes

1 ¼ cup whole milk

3 large egg yolks

¾ stick unsalted butter, cubed

Black sesame seeds

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. While potatoes are simmering, heat butter and milk in a small saucepan until butter is melted. Remove from heat and cover to keep warm. Preheat oven to 400°F with rack in middle. 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 well mixed. Spread about one-third of potatoes in a greased (butter or cooking spray) 1 1/2-quart shallow oven-proof 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.” Bake until tips of ghosts are golden and potatoes are firm, 20 to 25 minutes.