In a large pot, combine the apple cider, cubed pumpkin, and cranberries.
Add the cinnamon, nutmeg, allspice, and brown sugar (if using) to the mixture. Stir well to combine.
Heat the pot over medium heat until it begins to simmer.
Reduce the heat to low and cover. Let it simmer for about 30 minutes, allowing the flavors to meld.
After 30 minutes, use an immersion blender to puree the mixture until smooth. If you don’t have an immersion blender, carefully transfer the mixture to a regular blender in batches.
Return the smooth mixture to the pot. Stir in the vanilla extract and heat for an additional 10 minutes.
When ready to serve, ladle the poisoned apple cider into mugs or heat-resistant glasses.
Garnish each serving with a few blackberries and a sprig of rosemary for an eerie effect.
Notes
Serve the cider in spooky mugs, and consider adding dry ice in a separate container for a foggy effect, making it look like a bubbling potion!