Add the softened butter to the bowl of a stand mixer fitted with the paddle attachment. Beat it on medium speed for about 1 minute.
Add 2 cups of the powdered sugar, the salt, and vanilla extract. Beat on low speed until the powdered sugar is incorporated.
Add another 2 cups of the powdered sugar, along with the bourbon. Beat on low speed, and add the additional 2 cups of sugar as needed to thicken the frosting.
Frost your desired cake or cupcakes.
Notes: This recipe makes enough to frost 3-4 dozen cupcakes, depending on how heavily you frost the cupcakes.