'Butter bread' might be a dialect usage, perhaps, but for 'bara menyn' either 'bread and butter' or 'a slice of buttered bread' or even 'a sandwich' would be more usual. Or perhaps there is just a comma missing after bara and it is meant to be the two separate words.
brechdan is also used to mean a slice of bread and butter, but it is used more often for 'sandwich' nowadays.
Also, I would expect to see a mutation after a (and): bara menyn a chaws.
It seems that this sentence has been deleted from the course database due to its problems which were identified during the current beta testing. Unfortunately it has joined the ranks of the zombie phrases - Duolingo have not yet deleted them from the system for reasons beyond our control.