In a stand mixer with the whisk attached, beat the egg and sugar on high until you reach ribbon stage. This means when you can see the traces of the mixture when you most the whisk through it. It will take a good 4-5 minutes to reach this stage and it’s crucial – especially if you are not using baking powder, this is your only opportunity to get air into the mixture. Using a 20cm plate, draw 3 circles on your baking paper. Set aside. Combine the flour, salt and baking powder if using. Sift this into the egg mixture and very carefully fold to combine, using a figure of eight, until all the flour is incorporated. Be very gentle at this stage, but thorough. Pour the cooled, melted butter down the side of the bowl at the end and give a final few folds to incorporate it. Divide the mixture evenly between the 3 circles and gently use your spatulas to guide to the drawn edge. Bake in the oven for 5-8 minutes or until baked through and lightly browned. Allow to cool down. To remove from the baking paper, if it sticks, wet your hands and allow to damped the underside of the baking paper, this release the cakes. Trim any edges so you end up with 3 perfectly round and even sized bases.