Line a 12 case mini muffin tin with paper cupcake cases and set aside.
On low power in the microwave or using a double boiler melt 3/4 cup of chocolate chips until smooth.
Add a spoonful of chocolate to each cupcake case and drop the tin on the bench several times until the chocolate is smooth. Add a little more chocolate to each tin and carefully brush it up the sides a little, using a spoon. Also, try and make a small well in the bottom, being careful to make sure that the chocolate still covers the bottom of the case.
Put the tin in the freezer for 15 minutes while you prepare the peanut butter mixture.
Add peanut butter, softened butter & icing sugar to a small bowl and mix together really well until smooth.
After 15 minutes, remove the tin from the freezer and spoon a scant teaspoon of peanut butter mixture into each cup. Drop the tin on the bench a few times to flatten the peanut butter and put back in the freezer.
Add the remaining 1/2 cup of chocolate chips to the bowl and melt down again.
Once the peanut butter layer is hard, remove from the freezer and, working 3 at a time add enough chocolate to cover the peanut butter layer. Drop the tin on the bench again after each 3 to make sure the top chocolate layer is smooth.
Allow to chill in the fridge or freezer for 15 minutes until the top layer has set.
Store in the fridge, freezer or in an airtight container at room temperature.