so the a is skipped since "bara" ends with a?
This is just a guess, but maybe "menyn" can also be used as an adjective, like "chocolate" in "chocolate pancakes", so you get "bread with butter", "buttered bread".
I think you are right. Here: https://www.duolingo.com/comment/13178664
why does the " a " not get used ?
I'm confused by the missing "a" as well.
You don't say "Bara a menyn"?
It seems menyn is an adjective in this context.