Lightly frost the cupcakes with chocolate frosting.
Place a halved chocolate donut on each cupcake, & cover with frosting - leaving the center of the donut hole empty.
Dip the bottom edge of the frosted cupcake in red sanding sugar
Pipe green frosting into the center of the donut hole (I used a ziplock bag with the corner snipped off) letting it 'bubble' out for effect
Stick a small piece of cotton candy on the green frosting for cauldron smoke
Fit a licorice string over top for the cauldron handle, burying the ends in the cupcake
Pop a pretzel stick inside the donut hole for the cauldron stirrer