In the bowl of an electric mixer, beat butter until smooth and creamy. With the mixer on low speed, gradually add in sugar until it’s combined and all added. Add in vanilla and 2 tablespoons of bourbon, then increase the speed to medium-high and beat until fluffy, about 3-4 minutes. If the frosting still seems too thick (or you just, uh, want more booze), add in remaining bourbon and more if necessary.