I try not to boss people around too often, but desperate times call for desperate measures.
PUT BAKING POWDER ON THE SHOPPING LIST.
I find myself utterly perplexed by the size of baking soda and baking powder boxes/cans which say right on the label that they should be replaced frequently for best results.
Allow me to explain:
My previous batches of these super duper unbelievably amazing pumpkin mini muffins did not look like this. They did have the distinct "muffin top" that forms when batter rises above the top of the little crevice in the pan, but they did not puff like these beauties. They were slightly more dense, slightly less smooth on top. These, my friends, are perfect.
The difference? Finishing up my 2-year-old can of baking powder in this morning's pancakes and peeling the seal off of a brand new can just for these.
Please consider the age of your baking powder and baking soda. If they're old, perhaps its time to make a $2 investment and get yourself some new leavening agents.