This is a picture of the pan I use so you can see what it's like. I didn't have any lemon extract, so I substituted lemon juice for all the water, still added the 1 1/2 teaspoons of lemon juice in place of the extract, and put in the rind on one lemon. You could also (and I have before) substitute almond extract, or any other extract you have that you might think would be tasty. You could even add sprinkles or tiny chocolate chips in with the flour. If you wanted a chocolate sponge cake, add cocoa powder - about 1/4 cup - in with the flour. It might be a good idea to cut the flour by about 1/8 cup or so if you decide to do this so the cake isn't too dry.
The reason you invert the pan until it's cool is so that the weight of the cake will not make it collapse. I have done that before, and the cake is flat and very dense. Still edible, but not nearly as tasty. After the cake is cooled, you run a knife around the sides (if it hasn't fallen out by itself), take it out of the pan, and run the knife around the middle spindle and under the cake to remove the insert.
I always serve this with strawberries, fresh or frozen with sugar so it makes a syrup, chocolate sauce, because everything's better with chocolate, and whipped cream.
(It's really good sliced, toasted in the oven, and eaten at breakfast if you have any left over. I don't know how I know this. I, of course, always eat a well balanced meal for breakfast.)