In a medium mixing bowl, beat ½ cup of softened unsalted butter with 2 cups of powdered sugar until creamy, using an electric mixer on medium speed for about 2-3 minutes.

Gradually add 1 tablespoon of vanilla extract and 2 tablespoons of milk or heavy cream, mixing for an additional 2-3 minutes until the frosting is light, fluffy, and spreadable.

Divide the buttercream into separate bowls depending on how many colors you want to use. Add a few drops of food coloring to each bowl and mix well until you achieve vibrant hues.

Take your Chips Ahoy cookies and pair them by size, flipping one cookie from each pair upside down to create a sturdy base for the frosting.

Using a piping bag or a knife, generously pipe or spread a layer of your colorful frosting onto the flipped cookie.

Before the frosting sets, gently press candy eyes into the frosting on top of each sandwich to create little monster faces.

Let the assembled Cute Monster Sandwich Cookies sit at room temperature for about 15-20 minutes to allow the frosting to firm up slightly.

Once set, serve at any Halloween party or enjoy as a fun family treat.