Baking is a science, which allows for less improvising with a recipe compared to cooking. So when do you need baking powder ...

The double-acting nature of baking powder makes it an ideal choice for, say, cookies, which may have dough that needs to be chilled in the refrigerator before baking.

Here is what baking soda actually does for baked goods, how it reacts with other ingredients, ... Double-acting baking powder, which is the kind most often sold in stores, ...