It is possible that:
* There is a misunderstanding about the author's name or the title. Double-check the spelling and make sure you're not looking for a different work.
* The essay is not widely known or published. It could be a lesser-known or unpublished work by Serrano.
* The essay is not by Leopoldo Serrano at all. Perhaps you are confusing him with another writer or are misremembering the source.
To find the essay, try searching for it using different keywords or phrases. You could also try contacting literary institutions or libraries in Spain or Latin America, where Serrano may have lived or worked.
Please provide more information about the essay, like the date of publication or any specific context, and I can help you find it more effectively.