01 -
Preheat oven to 350°F (177°C). Lightly grease three 12-count mini muffin pans.
02 -
In a large mixing bowl, blend cake mix, eggs, oil, and black food coloring if using, until well combined.
03 -
Scoop approximately 1/2 tablespoon of dough into each mini muffin cup. Flatten the dough with fingers to prevent doming. Bake 8 to 10 minutes until edges are set.
04 -
Immediately after baking, use a 1 tablespoon measuring spoon to press an indentation into the center of each warm cookie cup. Allow to cool completely in pans before transferring to a wire rack.
05 -
Beat softened butter until creamy. Gradually add powdered sugar, vanilla, and salt; beat until smooth. Add milk tablespoon by tablespoon until buttercream reaches piping consistency. Mix in green food coloring to achieve desired hue.
06 -
Once cooled, pipe green buttercream into each cookie cup, filling to resemble bubbling potion.
07 -
Top each filled cup with round green sprinkles, candy eyeballs, Halloween sprinkles, and insert half a pretzel stick as a stirrer.
08 -
Serve immediately or store in an airtight container at room temperature for 3-4 days or refrigerated up to one week. Freeze undecorated cups up to three months, thaw before decorating.