Combine flours and baking powder in a bowl. Add club soda plus about 4 cups water. Mix into a smooth, fairly thin batter. Heat a large, non-stick skillet. When a drop of water bounces on the pan's surface, dip enough batter from the bowl to cover the bottom of the skillet, and pour it in quickly, all at once. Swirl the pan so that the entire bottom is evenly coated, then set it back on the heat.

When the moisture has evaporated and small holes appear on the surface, remove the injera. It should be cooken only on one side, and not too browned. If your first one is a little pasty and undercooked, you may need to cook a little longer or to make the next one thinner. But, as with French crepes, be careful not to cook them too long, or you'll have a crisp bread that may be tasty but won't fold around bits of stew. Stack the injera one on top of the other as you cook, covering with a clean cloth to prevent their drying out.