Simple chocolate cake

What ingredient makes a cake rise - baking soda or baking powder?
It's complicated and the short answer is both do. Baking powder is a combination of chemicals and doesn't require a reaction. Baking soda provides rise because of a chemical reaction with other ingredients (specifically acids) so requires an acidic ingredient in the recipe also (buttermilk, yogurt etc. or plain vinegar).

How do you make a chocolate cake moist?
For a moist cake, look for recipes using real chocolate, ground nuts and oil rather than butter. Also consider gluten free or flourless choc cakes for a super fudgy finish.

How can you make ahead and store this cake?
Cook and completely cool the cakes then wrap well in cling film and freeze for up to 3 months. Defrost at room temperature before decorating.

How do I stop chocolate cake from cracking?
Make sure the oven is at the right temperature (often happens if the oven is too high). If it rises too fast, it may dome and crack. Also don't over-bake the cake and make sure to bake in the centre of oven (though this is less of a problem in a fan oven).

How do I cover a chocolate cake with icing?
Start with a thin coating of icing (known as a crumb coat) then chill until the icing hardens. This will give a smoother surface to work with. Once chilled, coat roughly and fully in icing then use a cake scraper held at a 45 degree angle to smooth. A cake turntable also helps.