Red Velvet Starfruit Cupcakes and what the %#@!??

Ok, let's tackle this chocolate cake recipe thing again.
I went to the library and stocked up on cake books. I wanted to compare buttermilk chocolate cake recipes, see how everyone's are different. First off, they're all the same. Are your recipes really different when one calls for 8 oz chocolate and the other calls for 6 oz, but everything else is the same? Maybe, but seriously, I don't know how cook book writers don't deal with copy write problems more often.
In any case, this is the standard: chocolate, butter, sugar, eggs, flour, buttermilk. Ingredients vary slightly, but not enough to notice. Baking is more about the right texture, than about exact amounts most of the time. One day you'll need more flour or less because of a variety of reasons. So the recipes are really all the same. Except one I came across that wanted me to separate my eggs, and fold in the beaten egg white at the end. I thought, cool!, I'll try that. WRONG!!! Massive FAILURE. Someone with more egg chem. knowledge than me will have to explain why the cupcakes rose on the sides, but not in the middle. (Like they fell, but they actually never rose to begin with.) Also, all the recipes call for baking soda, which I used, and immediately regretted. Can you taste the baking soda in recipes? Nobody else seems to get what I'm talking about. But when you bake something that has baking soda in it, I'm telling you, it tastes awful, really sour.
Right, well. Back to the standard recipe, no separated eggs and baking powder instead this time. Seems to be going all right, and then this happens:

What the #&@%!?!?!?! Looks like I stuck my fingers in them, doesn't it. I didn't though! These cupcakes are from the last batch, where half turned out fine, and the other half did this. :P I'm blaming the oven - I cannot think of any other reason. Fortunately, most of the cupcakes turned out all right (not very domed, though. Any takers on reasons for that problem?) And they tasted amazing, and the frosting would have made up for anything. These are for you, Britt! Happy Bday through the nets. :D

Red Velvet Cupcakes
Adapted from the Magnolia Bakery Cookbook

8 oz chocolate, melted and cooled
2 sticks butter, at room temp
1 c sugar
1 c brown sugar
4 eggs
1 t vanilla
1 c buttermilk
1 T red food coloring
2 c flour
1 t baking powder
1/4 t salt

Cream the butter with the sugars until fluffy. Add the eggs one at a time, mixing well in between. Add the vanilla. Add the melted, cooled chocolate and the food coloring, mix until combined. Combine the dry ingredients; add the flour mixture and the buttermilk in thirds to the batter.
Bake at 350 F for 20 min.

Starfruit Buttercream

1 starfruit, peeled and pureed
1/2 c butter, softened
1/2 c shortening
4 c confectioners sugar
4 oz cream cheese, softened

Beat the butter and shortening until very light (about 5 min). Add the sugar slowly. Add the starfruit and cream cheese, and continue beating until very whipped.