Like the same way you'd write your name on a document, what is one ingredient you put on everything? Like one ingredient that could make some people you know "oh yeah *insert name here* made that". I'd say mine is cayenne. I put enough so you get that flavor, but so much that its spicy. Just to get that ooof flavor that elevates the dish. Cayenne is typically in a lot of dishes, so maybe its not the best example. But this is my signature ingredient.
