No substitute (Best Option)
N/ACrème Brûlée is a baked custard that relies on eggs, cream, sugar, and vanilla for its structure and flavor. Yeast is a leavening agent used primarily in bread and doughs to produce gas and rise, which is irrelevant here.
Attempting to add yeast or any leavening agent will negatively impact the custard’s smooth texture and classic dense consistency.
The final result remains a rich, creamy custard with a crisp caramelized sugar crust, exactly as intended without any yeast or substitutes.