In a medium mixing bowl, beat the softened butter and powdered sugar together using an electric mixer on medium speed until the mixture becomes light and fluffy, about 2-3 minutes.

Gradually add in 2-3 tablespoons of milk and 2 teaspoons of vanilla extract, mixing until the frosting reaches a creamy consistency that’s easy to spread.

Divide the fluffy frosting into separate bowls based on colors. Add a few drops of Halloween-themed food coloring to each bowl and stir well until vivid.

Match Chips Ahoy cookies into pairs based on size and shape, flipping one cookie upside down for each sandwich.

Spread a generous dollop of colorful frosting onto the flat side of the flipped cookie, then gently press the second cookie on top.

While the frosting is soft, press candy eyes into the frosting for a fun monster look.

Allow the assembled cookies to set for approximately 15-20 minutes and store in an airtight container.