Whisk together 2 cups confectioners' sugar, 3 tablespoons milk, 1/4 teaspoon anise extract and a pinch salt until smooth. The mixture should be just pourable, but very thick. Add up to 1 tablespoon more milk if needed, and a few drops more anise extract to taste, if desired. Use a spoon to drizzle the icing onto the cookies and spread with a small spatula or butter knife. Leave a border around the edges of the cookies; the icing will spread. Sprinkle with colored sugar or nonpareils if desired.