Beat butter for a few minutes with a mixer with the paddle attachment on medium speed. Add 3 cups of powdered sugar and turn your mixer on the lowest speed (so the sugar doesn’t blow everywhere) until the sugar has been incorporated with the butter. Increase mixer speed to medium and add vanilla extract, salt, and 2 tablespoons of milk/cream and beat for 3 minutes. If your frosting needs a more stiff consistency, add remaining sugar. If your frosting needs to be thinned out, add remaining milk 1 tablespoons at a time.