The first secret is melted butter. Make sure it is completely melted too, it seems to make a difference to the end result if there are just a few blobs that haven't melted completely.
Second is using an electric whisk for at least two minutes. This is best achieved in a food mixer, such as my best friend the kenwood chef, but you can use a hand held electrical whisk.
Another tip is bake in a low temp oven for a longer period. Our big sponges can take up to three hours to bake! You should test your oven to see what works best for you as every oven temp differs. In mine 160c is the best temp for sponges. I have had ovens in the past as low as 140c.
Last secret is to place a piece of greased greaseproof paper on top of the cake. This helps to stop the cake from drying out and the result is yummy moist sponge cake.
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