Albert Adria runs the pastry kitchen at el Bulli and has devised a method for microwaveable sponge cake. Instead of using traditional leavening agents (baking powder, baking soda), Adria loads his batter into an iSi food whipper and aerates it with N2O (nitrogen). The batter is dispensed into plastic cups that have a few slits cut in the bottom and cooked in a microwave for thirty seconds. Below is a recipe for a pistachio version.
Pistachio Thirty Second Sponge Cake
80 g pistachio powder (pistachios that have been run through a food processor and sifted)
80 g sugar
20 g all purpose flour
Combine ingredients and pour into food whipper. Load with 2 cartridges N2O. Dispense into a plastic cup (fill 1/3 of the way) that has a few slits cut in the bottom. Microwave at full power for 30 seconds.
el Bulli's version: chocolate sesame
In the image above, notice the size of the air pockets (much larger than you'd achieve in a traditional sponge cake).