Put the margarine, sugar, eggs, vegetable oil, cocoa powder, milk and self-raising flour in a large mixing bowl.
Mix to a smooth batter. I use an electric whisk for this, starting slow to avoid a flour cloud and then speeding up until the batter is light and airy.
Line a 12-hole muffin tray with cupcake cases and spoon the batter into them, levelling off.
Bake for 20-25 minutes until firm and springy on top. Transfer to a wire cooling rack and set aside to cool completely.
Make the toppers
Grab your black sugar paste. If it's stiff, knead it for a little while until smooth and mouldable.
Roll out to about 5mm (1/5 inch) thick.
Cut out 12 discs with your small scalloped cookie cutter. Remove the excess.
Use your icing pens to draw spider webs on top of the black discs of sugar paste. To do this, start by drawing four lines, each crossing in the centre to create a sort of asterisk, then draw concentric circles to complete the spider web affect. Set them aside to dry.
Make the frosting
Put the icing sugar, vanilla and softened butter in a large mixing bowl.
Start whisking slowly, speeding up until it comes together.
Add the black and purple food colouring.
Whisk again until you have a light, airy frosting that has noticeably increased in volume. If your frosting is too stiff, add a tablespoon of milk and beat again.
Assemble your cakes
Arrange your fully cooled cakes on a flat surface.
Transfer your frosting to a piping bag with a star nozzle. Now pipe tall swirls on top of your cupcakes
Straight away, before the frosting sets, add the spider web toppers.