You could just replace "egg yolk" with "egg yolk or a similar substitute" — this is actually what many "optionally vegan" recipes do. I mean, the Wikipedia page

You could just replace "egg yolk" with "egg yolk or a similar substitute" — this is actually what many "optionally vegan" recipes do. I mean, the Wikipedia page for cake also mentions eggs — are cakes made without egg considered not to be real cakes either?