In this essay, I will write about.

Or

The topic of this essay will be.

Such statements are considered amateurish, and most teachers will suspect the writer of trying to "pad" the essay--that is, adding irrelevant or redundant sentences to an essay in order to make it longer. Good writing works best when the reader forgets that he or she is reading and actually begins to experience what you've written. Mentioning yourself or your writing can get in the way of that experience.