While I liked the idea of making a huge batch of muffin mix, this mix wasn't our favorite. I personally would reduce the baking powder to 2 Tbls. (you could really taste it). It was also odd because one batch made 18 reg sized muffins, so I had to heat the oven (and kitchen) longer for an extra 6 muffins. I will probably just quadruple our regular muffin recipe in the future. Thanks for posting!
I just made these for the first time, although I used pear yogurt as I did not have plain, 2 teaspoons apple pie spice, and canola oil instead of butter. Made a lovely big muffin with excellent flavour and texture.