For the last few years I've been making a honey-raisin-spice quick bread for Imbolc. It was always tasty, but I had the hardest time getting the center to finish cooking before the edges got burned. I commented on the recipe, reminding myself to try adding more leavening next time.
After reading a section in Bakewise about chemical leaveners, I re-read the spice bread recipe. In Bakewise, Shirley says you need about 1 tsp baking powder or 1/4 tsp baking soda per cup of flour. (I'm sure this is only a general rule because I'm not done reading the book, especially the section on acids, which affects when bubbles are formed from the baking soda.)
The spice bread recipe called for 1 1/4 cup flour, 2 tsp baking powder, and 1/2 tsp baking soda. If Shirley's formula is right, then it should only need 1 tsp powder or 1/4 tsp soda. That's half of what the recipe calls for. Now, you may be thinking, like I was, that more leavening equals more bubbles and a bigger cake. However, Shirley points out that too much leavening can also result in flat or sunken cakes: the bubbles are formed and get so big that they escape the cake, leaving none left to lighten it.
That was apparently the problem for me. Today, I used 1 tsp baking powder and 1/4 tsp baking soda and ended up with flat, but not sunken, cakes.
With that combination of leavening, I only had to bake the cakes for the recommended time (43 minutes), so they didn't end up burned on the edges. I was very excited that my first application of baking math had fixed a recipe that I thought was terminally broken! So, without further explanation, here is the fixed recipe.