Ice-Cream Mask

This is an assembly instruction rather than a formula: a shell of lady fingers cemented with royal icing, built over a mould and then lowered like a lid over a brick of ice cream at the table. The hinge is that the icing must be fully hard before you attempt to move the shell.

• What a "brick" isA brick was ice cream frozen in a rectangular tin mould, commonly about a quart, turned out as a solid block and sliced across. A quart of firm ice cream packed into a loaf pan lined with plastic wrap and frozen hard gives roughly the same shape.
• The mould is only a formYou are building the shell on the outside of an inverted mould, not filling it. Choose something the same shape as the ice cream brick but slightly larger, and cover it in parchment or foil so the icing does not stick.
• Royal icing as cementRoyal icing here is icing sugar beaten stiff with egg white, used as glue and not as a coating. It sets hard at room temperature; pipe it in a thin line along each meeting edge. If the raw white concerns you, dried pasteurised egg white or meringue powder makes a very similar paste.
• "Through tube"A piping bag with a plain round tip about 1/8 inch across. A thick line will show as a ridge between the biscuits and stop them sitting flush.
• Trim the lady fingersCommercial savoiardi may be larger than the hand-piped biscuits assumed here. Cut them to the height of the mould with a serrated knife before assembling, or the shell will not stand square.
• Dry, not softLady fingers must be crisp for this. Any that have gone leathery will bow as the icing dries and the shell will collapse. Refresh them in a 300F oven for a few minutes and cool completely.
• Working timeAllow the shell several hours to harden, and keep it at room temperature rather than in the refrigerator, where the icing softens. Once lowered over the ice cream it should be served immediately, as condensation will soon soften the biscuits.
• YieldA shell over a quart brick would serve perhaps six to eight, one slice each with a piece of the biscuit shell.