Simple answer: with your mouth of course.
This of course is not real. It’s a creation by one of those food replica companies which make those sample displays (aka 食品サンプル or shokuhin sanpuru) located outside many eateries in Japan.
Often times, the samples are more expensive than the actual dish. The cheaper replicas like the ones found at some souvenir shops along Asakusa’s Kappabashi-dori, are often times geared towards tourists, and therefore, are easy to tell they are fake. The above was a well made sample on display at one of those Kappabashi-dori shops. For restaurants which want their dishes presented as well as the real thing, well, the attention to detail at the high end is amazing.
The above clip briefly shows how some items are made but if you browse through the related videos, there are more detailed ones.
