I've always loved baking but never learned the science behind it. I'm reading about the why's and how's of using baking powder and baking soda and starting to understand when and why to use each one. In general, most sources I've seen so far recommend using 1 tsp. BP for each cup of flour. Now I'm assuming that's a general recommendation when the recipe does NOT include BS, since one source I just read says to "use about ½ teaspoon baking soda and ½ teaspoon baking powder for each 2 cups flour" If I followed the general guidelines noted earlier, I'd use 2 tsp. BP. I found a blog recipe for lemon blueberry muffins using sour cream, yogurt, 1/4 C lemon juice, and blueberries (i.e. lots of acids + heavy additions). The recipe calls for 2 cups of flour, 1/2 tsp. BP, but no BS. Based on my reading so far, I'm considering changing the leavening to 2 tsp BP and 1/4 BS. However, I'm still not clear on how much BS to use when adding acids not included in the original recipe. If I use brown sugar instead of white, or yogurt instead of plain milk, how much BS should I use for each cup of flour --- and is this determined by the BP already in the recipe?