Hello, I’ve been trying to make a jelly roll cake recipe from Great British Bake Off-it seems like a chiffon style recipe in that it has no flour, used melted butter and cocoa, and the yolks are whipped separately from the whites. Each time, it’s been very very flat. The first couple times the bottom was rubbery. I concluded that maybe I was overbeating the eggs because it was difficult to fold the whites in and I had a lot of lumps, so I stopped whisking earlier this last time. It seemed easier to incorporate the whites, but my cake was still extremely flat. Did I underbeat this time, or is something else wrong?

Actually, you cake is supposed to be pretty flat, not more than 1/2 inch thick, otherwise it will not roll.  How did it taste?  There is a possibility that you did everything just right.