Creating Frankenstein Cookie Bars is a fun and straightforward process that anyone can enjoy. Follow these easy steps to create your own spooky treats:

1. Preheat the Oven: Start by preheating your oven to 350°F (175°C). Grease and line a 9×13 inch baking pan with parchment paper for easy removal later.

2. Cream Butter and Sugars: In a large mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until the mixture is light and fluffy.

3. Add Eggs and Vanilla: Blend in the eggs, one at a time, then add the vanilla extract. Ensure everything is well combined.

4. Mix Dry Ingredients: In a separate bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt.

5. Combine Wet and Dry Mixtures: Gradually add the dry mixture to the wet mixture, combining them thoroughly until you have a smooth dough.

6. Add Food Coloring: Stir in the green food coloring until the dough reaches an even, vibrant shade of green.

7. Fold in Chocolate Chips, Nuts, and Marshmallows: Gently fold in the chocolate chips, chopped nuts, and mini marshmallows until evenly distributed.

8. Spread the Dough: Pour the dough into the prepared baking pan and spread it evenly. Make sure to smooth the top with a spatula.

9. Bake: Place the pan in the preheated oven and bake for 25-30 minutes, or until the edges are golden brown, and the center is set.

10. Cool: Remove the pan from the oven and allow the cookie bars to cool in the pan for about 10-15 minutes before lifting them out using the parchment paper.

11. Cut and Decorate: Once cool, cut them into squares or rectangles. Place edible eyeball candies on top to give them a spooky look.