01 -
Preheat the oven to 350°F. Lightly grease three 12-cup mini muffin pans.
02 -
In a large bowl, combine cake mix, eggs, canola oil, and black food coloring if using; mix until smooth.
03 -
Scoop about 1/2 tablespoon of dough into each muffin cup and gently flatten the surface with your fingertips.
04 -
Bake for 8 to 10 minutes until edges are set. Remove from oven and press the back of a tablespoon into each cookie to create an indentation. Cool completely in the pans.
05 -
Beat softened butter in a medium bowl until creamy. Gradually add powdered sugar, vanilla extract, and salt. Add milk gradually, mixing until smooth and pipeable. Tint with green food coloring to desired hue.
06 -
Pipe the green buttercream into each cooled cookie indentation, filling it to resemble bubbling potion.
07 -
Top each cookie with green sprinkles, Halloween sprinkles, and candy eyeballs. Insert a halved pretzel stick into each as a stir stick.
08 -
Arrange cookies on a serving platter and present.