Take the butter out of the fridge at least 1 hour beforehand. Break the eggs then weigh 125 g butter carefully; this is important for the rest of the recipe. Put into a bowl and leave at room temperature for at least 1 hour.
3: Start beating and mix the sugar and butter thoroughly.
4: Add the eggs one at a time...
5: ...and beat until the mixture is smooth. Important: If the mixture begins to curdle, stop beating and plunge the bowl into a pan of hot water, beating with a hand whisk until the mixture homogenizes (normally about 1 minute).