Making chocolate Swiss roll is a bit tricky. Why? Because cocoa powder complicates things. If you want a straightforward recipe, go for vanilla roll. That's almost idiot-proof (not that idiots are the lowest common denominator).
Cocoa powder makes the cake less stretchable, so you have to be careful not to overbake the cake. Even slight overbaking makes the cake crack when you roll it.
Cocoa powder also makes the crust sticky, so you have to be careful not to underbake the cake. The more underbaked the crust is, the stickier it is.
The cake is perfectly done when it just turns springy in the middle. After it's cooled down, the crust should be a bit sticky around the edges. That's OK because the ends will be trimmed, or tucked inside/below after the cake is rolled.
If the entire crust isn't sticky, that's not a good thing at all. The cake is too dry and will likely crack when you roll it.
If the entire crust is sticky, it's gonna stick to whatever it rests on. Of course, that's not a problem if you ice the cake. Or if you go for the skinless look and roll the cake inside out.
Even when you've got the cake baked just right, you may still have a problem when you're rolling the cake. Why? Because the crust doesn't really stick to the crumb, so it comes off very easily. The loose crust is caused by cocoa powder which, as I said, complicates things.
Chocolate cakes have haphephobia (fear of being touched). Direct contact with the crust must be minimized if you don't want to damage it. How? Like this:
⋈ Put the cake on a piece of parchment paper, face down. Spread with whatever filling you like.
⋈ Start rolling the cake by making a fold in the cake. The fold must be very small, or the cake will be oval instead of round after rolling.
⋈ After the first fold is tucked in tightly, lift and tilt the parchment paper with your left hand (if you're right-handed). As the cake moves forward, it may bulge here and there. Gently flatten the bulges with your right hand so that the roll is tight and even. If you're making a very long roll, you'd need a rolling pin (or the core of your parchment paper or aluminium foil) to do this.
Because the cake doesn't handle well, it cracks (when you roll it) if it's too thick. And if it's too thin, the inside may be too dry when the crust is just right. Hence, you must scale the recipe according to your pan size. You don't want too little or too much batter in the pan.
Why make such a fuss over a cake? Why not just let it crack? You can hide the cracks with icing, icing sugar, chocolate rice/shavings, nuts, whatever. Nobody would know, right?
Yup, covering up is an easy way out. But you'd have bought a chocolate Swiss roll if you had wanted the easy way out. Or at least made a Swiss roll without cocoa powder. Or just eat the bloomin' cake without rolling it!
For those who want to make a good but uncomplicated Swiss roll, click here for my vanilla recipe. For those who want to make a chocolate roll for the sake of making it, because eating is only half the fun: