First, you could read our guide on descriptive essays: https://academichelp.net/academic-assignments/essay/write-descriptive-essay.html
Secondly, try to remember that it has an introduction, body paragraphs, and a conclusion. However, your thesis statement will not be assertive. Do your best to describe your favorite dish in all its specifics. You can detail its history first, like how the dish came into being throughout history. Next, you could describe its particular ingredients, the way it is presented, and the way it is cooked.