Here is the sentence:
When you list grammatical items, you must use parallel structure. Here, barbecued ribs and potato salad are both modified by possessive nouns, Grandma's and Aunt Sally's. But heaping plates of jiggling banana Jell-O prepared by Cousin Sue ruins the parallelism. Well done, grammar gourmet!
To fix the problem, Cousin Sue's banana Jell-O is all you need.