This cake was made with Copy-flex, a food grade silicone that is ideal for very detailed casting, since in its liquid state it is very fluid and it seeps into every single nook in your negative. For this mold I made the negative simply out of Plexiglas rectangles glued together with acrylic glue. It is key to make sure that the negative is on a flat surface, well adhered (i spread a thin layer of shortening on the base to keep it steady; some use Vaseline, but Vaseline should really have no place in a kitchen... I suppose neither should shortening for the matter). As you can see from the website you combine both compounds and immediately pour them onto the negative or the mold you are using. It takes a few hours to set but the results are always breathtaking to me. This silicone is heat and freezer resistant.
Oh and the cake, if you want to know, has the following components: Yuzu cream, litchi jelly, vanilla streusel and vanilla genoise as a base.
On a final note, Copy-flex can be costly (and a pain to cleanup), but worth it if you ask me.