Serradura, a dessert that originated in Portugal and is popular in Macau, is made by layering whipped cream sweetened with condensed milk and pulverized Marie biscuits (serradura translates as “sawdust”). It inspired this frozen sweet that looks impressive but is a breeze to make. We keep the biscuits mostly whole and layer them in a pan with fruit-studded cream; after freezing, the “pudding” is cut into slices that reveal a mosaic-like design. For serving, you can invert the semifreddo onto a platter or slice it directly in the pan; if too firm to cut, let it soften for a few minutes at room temperature.