Substituting leaveners is a tricky task. Here are some tips for doing it well.
Our favorite is instant yeast (also sold as rapid rise yeast and bread machine yeast) because it is fast acting and can be stirred directly into the other dry ingredients. Active dry yeast, on the other hand, must be dissolved in warm water (around 110 degrees) before being added to the rest of the ingredients. Other than the method of incorporation, instant and active dry yeast are interchangeable.
All chemical leavening is based on the reaction of an acid and a base, or alkali (almost always baking soda), to produce the carbon dioxide gas that makes the baked good rise. Baking powder contains an acid along with baking soda and a small amount of cornstarch to absorb moisture and keep the mixture shelf-stable.
To Replace: 1 teaspoon baking powder