Put all the ingredients into a bowl and mix them together. It's easiest to use an immersion blender and a tall immersion blender jug. Pour the mixture through a fine-mesh sieve because it is crucial to avoid lumps. They will clog your siphon bottle. Put the cap on the bottle and give it two shots with gas cartridges. Shake the siphon vigorously. Make a couple of holes in the bottom of a paper cup (I usually use a meat skewer for this). Spray the contents from the siphon bottle into the cup. Only fill the cup 2/3 of the way with the batter. Cook it for 50-60 seconds at full power in the microwave. Take it out and turn it upside down on a rack to cool for 1-2 minutes. Use a regular knife and cut down both sides so it releases, and voila, you have a nice sponge cake. Continue the process with the other paper cups. I think it is best enjoyed when torn into pieces and placed in various spots on a dessert plate, somewhat like in this recipe: Espresso pasta with foam and chocolate cake. Bon appétit.