In a large mixing bowl, beat the softened butter on medium speed for 1-2 minutes until creamy and light in color, releasing a rich, buttery aroma.
Sift the powdered sugar to remove any lumps, then gradually add it to the butter, about 1 cup at a time, mixing on low speed to prevent a cloud of sugar from forming. Continue until the mixture is smooth and fluffy, about 2-3 minutes.
Add a pinch of salt and the vanilla extract, then mix on medium speed for 30 seconds until combined and fragrant.
Pour in 1-2 tablespoons of milk, then beat on low speed to incorporate, gradually increasing to medium-high. The frosting will begin to turn glossy and silky, feeling smooth and slightly thickened, about 1 minute.
If desired, add a few drops of gel food coloring and gently mix until the color is evenly distributed, watching for a vibrant, uniform hue.
Check the frosting’s consistency: it should hold its shape when piped but spread smoothly. If it’s too stiff, add a tiny splash of milk; if too runny, sift in a little more powdered sugar and mix well.
Let the frosting rest for 10 minutes to allow it to settle and release any air bubbles, which helps achieve a flawless finish.
Once ready, pipe or spread the frosting onto cooled sugar cookies, using a piping bag for detailed designs or an offset spatula for smooth surfaces.
Allow the decorated cookies to sit at room temperature for 20-30 minutes, letting the frosting set with a shiny, velvety finish before stacking or serving.
