Arrange the two-bite brownies on a serving tray or clean work surface.
Pipe or spoon purple and green icing onto the top of each brownie. Add a generous amount so it looks like a colourful, bubbling witch’s potion. It can spill over the sides.
Break the pretzel sticks into smaller pieces, if needed, and carefully place them into the icing to look like little stirring sticks.
While the icing is still soft, add Halloween sprinkles and candy eyeballs. Mix and match the decorations to make each cauldron a little different.
Allow the decorated brownies to sit in the fridge for about 20 minutes so the icing and decorations can settle into place.
Enjoy this easy and spooky Halloween treat!