Preheat your oven to 350°F (175°C) and lightly grease three mini muffin pans.

In a large mixing bowl, combine the cake mix, eggs, oil, and optional black food coloring. Mix until smooth.

Scoop about ½ tablespoon of cookie dough into each muffin cup and press down to flatten.

Bake in the preheated oven for 8–10 minutes until edges are set and tops are slightly puffed. Press an indentation in each warm cookie.

Allow the cookie cups to cool for 10-15 minutes, then remove from pans and place on a wire rack.

Beat the unsalted butter until fluffy, then gradually sift in powdered sugar and mix well. Add vanilla, salt, milk, and green food coloring, whisking until smooth.

Using a piping bag, pipe the buttercream into the center of each cooled cookie cup in a swirling motion.

Decorate with green and Halloween sprinkles, candy eyeballs, and pretend pretzel stirrers.

Serve on a festive plate or tray to enjoy at your Halloween gathering!