On medium-high heat, in another sauce pan, melt butter. Add onions and cook, stirring occasionally, until soft and translucent, about 3-4 minutes.
Add sake or white wine, and whisk, scraping any brown bits off bottom. Add in chicken broth and let come to a boil for a minute. Add in cream and let come to boil about 30 seconds-1 minute more until thickens.
Add chinese five spice seasoning, followed by salt and pepper to taste. Put in another good dish for dipping crab.
Set crab and dipping sauces on a wooden cutting board of some sort, and enjoy!