I left the cakes in just a hair too long. They came out fine, but not quite as moist as they could be. I think I need to not be fooled by the bottoms of sections looking not-done and trust the toothpick test. Not using the real icing probably also affected the moistness; the real boiled icing tends to soak into the layers of the cake, which is what makes the whole thing so moist and perfect.
But I failed again in making the icing. Three times. The first time, I had mis-copied the recipe, and put 1/4 cup (!) of cream of tartar in the icing, rather than 1/4 teaspoon. The second time, I used the regular beaters rather than the aerator attachment to beat the egg whites, and didn't get them fluffy, resulting in the same failure mode as my attempt at apc9: runny liquid egg whites with lumps of congealed hardball in them.
I came within inches of getting the third attempt just right, when disaster struck. I whipped the bejesus out of the egg whites, and got them all frothy and whipped. The boiled portion was juuuuuuust about ready to come off the stove, when all of a sudden, it carmelized and started emitting huge clouds of billowing black smoke! I felt like a shoujo anime heroine -- the type who always wants to make something delicious for her love interest, but is woefully inept in the kitchen.
Since the whole house was filled with smoke and generally smelled like a marshmallow that had been dropped into the campfire, Peri vetoed attempt #4, and I had to settle for running out to Weggies for a can of store-bought chocolate frosting. We wound up with a decent cake that was an improvement over box cake -- and Matt ate two big slices -- but I still have yet to successfully produce the family recipe. Maybe I'll try again when Amanda gets here later in the week.