[header] How to make gyudon [title] Slice the beef and vegetables. [step] Use a sharp knife to shave the beef into very thin slices. Cut the onion and shiitake mushrooms into moderately thin slices, as well. 
[substeps] To save yourself time and effort, ask the butcher to slice the beef very thinly before packaging it. If the butcher does not slice the beef, freeze it for 1 hour before slicing it yourself.