Using electric beaters, whisk together the whole eggs, yolks, sugar and a pinch of salt until pale and moussey (the mixture should almost double in volume), this will take 3-4 mins. Gently fold in the melted chocolate and butter, and then the flour, being careful not to knock out too much air. Spoon into the prepared moulds, stopping just shy of the top. Chill for at least 1 hr.