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

Gradually mix in milk and vanilla extract, continuing to beat until well-combined and creamy.

Divide the frosting into separate bowls and add Halloween-themed food coloring; mix thoroughly.

Match Chips Ahoy cookies into pairs; flip one cookie upside down to prepare for frosting.

Pipe or spread frosting on the flat side of the first cookie in each pair, then sandwich it with the second cookie.

While the frosting is soft, press candy eyes into the sides, arranging them playfully.

Allow the cookies to set at room temperature for 10-15 minutes.