In a medium mixing bowl, beat 1 cup of softened unsalted butter and 4 cups of sifted powdered sugar together until light and fluffy, about 3-5 minutes. Add 2 teaspoons of vanilla extract and 2-3 tablespoons of milk or heavy cream, mixing until well combined and creamy.

Divide the frosting into separate bowls, adding a few drops of food coloring to each and mixing thoroughly.

Choose your cookies and match them in pairs, flipping one cookie in each pair upside down.

Pipe or spread a generous dollop of frosting onto the flat side of the upside-down cookie, then gently press the second cookie on top.

Press one to three candy eyes into the frosting before it sets.

Allow the frosting to set for about 15-30 minutes at room temperature.

Once set, serve and enjoy your Monster Sandwich Cookies at any Halloween gathering!