Preheat oven to 180C/160C fan-forced. Line two 12-hole, 1/3 cup-capacity muffin pans with paper cases.
Prepare packet cakes following packet directions. Spoon 1/4 cup batter into each paper case. Bakie for 25 minutes or until cooked through. Stand in pan for 5 minutes. Transfer to a wire rack to cool completely.
Make icing: Using an electric mixer, beat butter in a bowl until pale. Gradually add icing sugar mixture and milk, beating constantly until combined.
Spoon icing into a piping bag fitted with a 1cm fluted nozzle. Pipe small rosettes over half of the cakes to cover. Sprinkle with cachous.
Using a small sharp knife, cut a 1.5cm deep round from centre of each remaining cake, 1cm in from edge of cakes (see Cooking class, below). Cut rounds in half to form butterfly wings. Pipe a little icing into cavity of each cake. Arrange 'butterfly wings' on icing. Spoon jam into a piping bag fitted with a 2mm plain nozzle. Pipe a small amount of jam next to icing. Dust with icing sugar. Arrange cakes on a cake stand. Serve.
