Put a 9-inch springform pan in the freezer for 15 minutes. Meanwhile, let 1 container vanilla ice cream soften at room temperature.

Remove the pan from the freezer. Spread a 1/2-inch-thick layer of softened vanilla ice cream on the bottom and up the sides of the pan. (If the ice cream gets too soft, return to the freezer.) Freeze until firm, about 45 minutes.

Meanwhile, pulse the chocolate wafers in a food processor to break into large crumbs. Add the chocolate shell topping and pulse until the crumbs are moist, about 5 pulses; set aside.

Let the chocolate ice cream soften at room temperature, about 15 minutes. Spread over the vanilla layer, firmly packing the ice cream into the pan. Spread the chocolate crumb mixture over the chocolate ice cream. Freeze until set, about 1 hour.

Remove the remaining container vanilla ice cream from the freezer 15 minutes before assembling the final layer. Spread the ice cream over the crumb layer, packing it tightly, then smooth the top with an offset spatula. Freeze until firm, about 2 hours.

To unmold, wipe the outside of the pan with a hot cloth, then run a hot knife around the inside; unlatch and remove the side. If the ice cream cake is too soft, refreeze 20 minutes.

Spread 3 cups whipped cream over the top and sides of the cake. Freeze until set, about 20 minutes. Put the remaining 2 cups whipped cream in a pastry bag fitted with a star tip; pipe along the top and bottom edges of the cake and decorate with sprinkles. Return to the freezer; remove 15 minutes before serving and slice with a hot knife.

Photograph by Steve Giralt