To make frosting for Christmas cookies, you'll need powdered sugar, butter, milk, vanilla extract, and a little salt. First, sift the powdered sugar into a large mixing bowl. Then, beat in the butter until the mixture is smooth and creamy. Gradually add in the milk and vanilla extract, mixing until the frosting reaches the desired consistency. Lastly, stir in the salt and use a spatula to spread the frosting onto your cookies. Enjoy!