Cream the butter and sugar together then add the vanilla and mix.
Add 1 egg and a few spoons of sifted flour. Then add the other egg and the remaining flour and mix well. Add a little milk to get a good dropping consistency.
Line a 12 hole muffin tin with Halloween paper cases. Divide the mixture into the cases and bake in the oven for around 15 minutes (check after 10 minutes to allow for oven variations).
To decorate:
Cream together the icing sugar, butter, vanilla essence, milk and coco powder until smooth.
Mix up the jelly to create a lumpy texture.
Scoop out a piece from the centre of each cupcake to make a cauldron.
Spoon the jello into the hole in the middle of the cakes.
Pipe the icing around the rim with a syringe or piping bag.
Add some Halloween- themed jelly sweets to the green 'slime' in the cauldron to finish.