Sift the dry ingredients into a bowl. Add the butter and beat in a food processor until mixed.
Beat the wet ingredients together and slowly add to the dry ingredients and butter until fully mixed.
Fill cupcake cases just over halfway with the mixture and place in an oven preheated to 170C (325F) Gas 3 for 20-25 minutes or until a skewer comes out clean.
Leave to cool on a wire rack.
In the meantime make the icing by beating together the butter and sifted icing sugar together until soft. Add the milk to achieve the right consistency. Put the icing into a piping bag and pip on top of the cupcakes.
To decorate split the Oreo cookies in half and place in the middle of the icing. Add spider legs with the chocolate writing icing and eyes with the white and black writing icing.