Pre-heat your oven to 140C Fan/325F/Gas Mark 3, and line a cupcake tin with cupcake cases (ideally black ones)
For the cupcake sponge, mix together the baking spread and caster sugar, ideally using an electric mixer, for 5 minutes until smooth and fluffy
Add the eggs and vanilla extract and whisk them in well
Then gently whisk in the self raising flour
Add the black food colouring and mix in well
Divide the mixture between the cupcakes cases, and bake them for 25-30 minutes or until a skewer inserted in the centre of the cupcakes comes out clean. Put them on a rack to cool completely
Once the cupcakes are fully cool, use a cupcake corer or a knife to make holes in the middle of each cake
Add a little bit of green food colouring to the custard and mix it in, then spoon it into each cupcake
Make the buttercream by mixing together the butter and icing sugar until smooth, then add the vanilla extract, milk and the green and yellow food colourings until you have a bright green colour. You can add more milk if the buttercream is too stiff
Using a piping bag, pipe the buttercream onto the cupcakes. Or spread it on with a spoon. Decorate with the candy eyes and sprinkles
Store in an airtight container in a cool place, eat leftovers within 3 days