01 - In a large mixing bowl, beat the softened butter with an electric mixer on medium speed until smooth and creamy, about 1 minute.
02 - Gradually add the powdered sugar, beating on low until incorporated. Scrape the bowl as needed to ensure even mixing.
03 - Add the milk, vanilla extract, and salt. Beat on medium-high for 2–3 minutes until light and fluffy.
04 - For a thinner consistency, add more milk, 1 teaspoon at a time. For a firmer frosting, add a little more powdered sugar.
05 - Spread or pipe onto completely cooled sugar cookies. Allow to set at room temperature for 1–2 hours for a slight crust.