Green and yellow gel food colouring to get the desired colour.
For the frosting
½teaspoonvanilla essence or vanilla sugar
A pinch of salt
2 ½cupsicing sugar
Blackpurple, orange or green gel food colouring, as you wish
For the decoration
For the cupcakes
Preheat oven to 175°C. Line two 12-count muffin pans with patty pans.
Beat the egg whites on high speed in a medium bowl until soft peaks form. This should take about 2-3 minutes.
Sift the flour, cornstarch, baking soda, cocoa powder and salt together in a medium bowl to make sure they are evenly combined. Sifting the mix three times should be sufficient. Set aside.
Beat the butter on high speed until smooth and creamy – about 1 minute. Add the sugar and beat on high speed for 2 minutes until creamed together fairly well. Scrape down the sides and up the bottom of the bowl with a silicone spatula as needed. Add the oil and beat on high for 2 minutes. The butter may look "lumpy” and not completely combine with the oil. This is normal.
Add the egg yolks and vanilla. Beat on medium-high speed until combined. Scrape down the sides and up the bottom of the bowl with a silicone spatula as needed. Beat in the vinegar and the food coloring– until you reach your desired colour.
With the mixer on low speed, add one-third of the dry ingredients, then half the buttermilk, and alternate until all the dry ingredient mix and buttermilk have been added. Mix each addition just until incorporated. Do not overmix.
Fold whipped egg whites into cupcake batter with a silicone spatula or wooden spoon. The batter will be silky and slightly thick.
Spoon batter into cupcake liners filling 1/2 – 2/3 of the way full. Bake for 20-21 minutes or until the tops of the cupcakes spring back when gently touched and a toothpick inserted in the centre comes out clean.
Allow to cool in the pan for 5 minutes, then transfer to a rack to cool completely.
For the slime
Pour milk into a saucepan and add the vanilla paste. Warm over medium heat until it is just about to boil. Remove from heat and allow to cool a little (2 minutes).
Whisk the egg yolks and sugar together in a heatproof bowl until well combined and it thickens and turns a pale yellow.
Add the cornflour and stir until well combined.
Pour about 2 tablespoons of the milk into the egg mixture and stir well. This will help temper the eggs. Add a little more and do the same. Finally, add the remaining milk and stir until it is well combined.
Pour back into the saucepan and heat over medium heat, stirring consistently, until the mixture starts to thicken.
Remove from the heat and stir in butter until it is all melted. This will make it glossy.
Add the food colouring until the desired shade is obtained. I had about half a teaspoon each of the green and yellow food dye.
Cover with plastic wrap so that the wrap is touching the slime. Allow to cool and then refrigerate until cold.
For the frosting
Put the butter and cream cheese in the bowl of your stand mixer (paddle attachment) or a bowl with your hand mixer and beat until well combined and a little fluffy.
Add the vanilla and salt and mix to combine.
Add one cup of the icing sugar and combine, then add the more, a half or third of a cup at a time, until the right consistency is reached.
Add the food colouring in the colour you have suggested until you reach the desired hue.
Using a spoon, take the 'hat' off the cupcake. Spoon some slime into the hole and replace the hat.
Frost the cupcakes so that the slime is hidden.
Add the cobwebs.
For the cobwebs
Melt the marshmallows in the microwave for about 20 seconds or until just melted. Allow the marshmallows to cool just a little then dip dipping your thumb and index finger into the marshmallows and open and close your fingers until the marshmallows become stringy.
Once stringy, stretch small amounts to form the 'webs' and droop over the cupcakes. They will be very sticky!
Add as much or as little of the food colouring as you wish to reach the depth of colour you seek. I prefer to use gel colouring. I have used liquid food colouring, but found that I needed much more for a much less vivid result. The cupcakes were dark grey instead of black.Sally has a number of additional tips on her blog. Instead of repeating them here, please just look at her post.For the slime: if you'd prefer, make orange or bloodred slime.