Both layers are really thin. I used an 8x3 pan instead of 8x2. Would that make a difference?
I believe the only leavening agent in that cake is baking soda. When you use soda, you have to be fairly quick getting the product into the oven, because the chemical reaction which produces rise begins happening the minute it comes into contact with the acid. Your pan height would not affect it, as the actual width is still the same 8 inches. I think you just had a delay in baking which let too much gas escape before the structure of the cake set enough to trap it. It's also possible that your batter was too thin, which would also let the gas escape more easily. Providing your measurements were accurate, it may be due to having flour which was a bit damp, and unable to absorb as much liquid as it normally might. On humid days, it may require a bit of tinkering- sometimes just adding another tablespoon of flour to adjust a batter thickness will do the trick. Otherwise, when you are working with baking soda, you need to have both pan and oven ready to go, mix quickly and get it into the oven. Otherwise, you do get flatter results.
Thanks for the info. I don’t think think I delayed getting it in the oven but maybe i did. I put that cake in the freezer and made Bravetart’s Devils Food Cake today. I’m much happier with this cake.
What kind of cocoa did you use?
I'm asking because I think the Dutch processed cocoa is an error. DP cocoa is neutral, pH of 7. I don't see anything acidic, other than coffee, to react with the baking soda (an alkali) for leavening. If you used DP cocoa and boiling water, that might be why your cake didn't rise; no acidic component to react with the baking soda.
I used Cacao BarryExtra Brute, which is what Stella Parks recommends. The label doesn’t say Dutched but it does say alkalined. I made Bravetarts Devils food cake today and it turned out great.
Did you use water or coffee? That may have been the difference. The coffee would have reacted with the baking soda and the water would not.
I used half water and half coffee. I’ve made this cake successfully several times. I don’t know why it was a dud this time.
Is there a chance your baking soda has expired? I got caught by that once. Make that twice. Scientific method, you know.