Thanks everyone for all the input. Diane, I *might
* be able to make cake pops out of the ruined cakes if my boys and I would stop eating from the cake scraps bucket. There may not be anything left by tomorrow.
Thanks for the info BakingIrene. I looked at the ingredients for the jimmies, and when I saw that two of the top three ingredients were sugar and oil, I thought they may have thrown off my ratios. But you are right, they don't dissolve into the cake batter, although they do add more volume for the structure to support. When this is over, I'm going back to the plain recipe without the jimmies and I will test it to see if I'm having trouble without them, especially if it's the buttermilk.
You know southerncross, making my own baking powder isn't a bad idea. I make most of my own stuff as it is, so that would just be one more thing to have greater control over. Thanks for the heads up.
No anavillatoro1, I haven't tested the oven temperature - yet. Even if that isn't the problem this time around, it's a good "regular maintenance" task I should do from time to time. Thanks for the reminder.
And thanks to you AuntGinn for keeping up CC's spirit of helpfulness!!
I really appreciate all of you guys!