Place the butter and dark chocolate in a saucepan over a very low heat and stir occasionally until melted.
Stir in the crushed popcorn and biscuits and mix well. Put the mixture into a separate bowl to cool completely, then chill for about 30 minutes until firm enough to form into balls.
Divide the mixture into 12 portions and form each portion into a smooth ball. Carefully push a cake pop stick into the centre of each ball, moulding it onto the stick as you push. Arrange on a plate covered with greaseproof paper and chill for about an hour until firm.
Put the milk chocolate and white chocolate into separate heatproof bowls over 2 saucepans of just simmering water until melted. Remove the bowls from the pans of water and cool for 10 minutes.
Working on one popcorn pop at a time, hold over a bowl of chocolate and spoon the melted chocolate over the pop, turning to coat completely. If the popcorn pop comes off the stick, dip the end of the stick into the melted chocolate and then push it back into the centre of the ball.
Tap the stick gently on the edge of the bowl to remove any excess chocolate and then stand upright in a cake pop stand or tall glass while you prepare the other popcorn pops. Keep any leftover chocolate and leave the pops in a cool place to set.
To decorate, re-melt the leftover chocolate if necessary, and use a little to secure a wafer butterfly to each popcorn pop. Leave for a few minutes to set before serving.