Whisk the eggs and sugar together in a bowl over a pan of hot water. Continue to whisk until the mixture has doubled in volume and is light and creamy. Remove from the heat and continue to whisk until cold and thick. This is called the ribbon stage as the mixture will trail off the whisk in ribbons when you lift it out of the mixture. Lightly fold in the flour and melted butter. Gently pour the mix into the prepared tin and
Allow to cool for 10 minutes in the tin and then turn out on to a wire rack.