My first attempt to make this and the sides/edges turned rubbery. A cross section of the cake showed uneven air release because there were air tunnels leading up, sort of like termite tunnels. What could have caused this? I followed the recipe to the letter. The only thing I can think of is that that maybe I should have sifted the dry ingredients together 3 times. I only did it once per the recipe. Also, my baking powder is old. I bought it a year ago... could it be that it has lost its potency and caused the rubberiness?