Melt half the chocolate and pour it equally into the bottom of a lined cupcake pan.
Tap on a surface to flatten the mixture and freeze for 15 minutes.
Beat the peanut butter, icing sugar and butter together until light and fluffy. Spoon it on top of the chocolate and tap again to flatten. Freeze for 15 minutes.
Melt the remaining chocolate and pour it over the top to finish. Tap again and freeze for 15 minutes.