Start with making the Butterscotch sauce. In a small saucepan, melt the butter. Add the brown sugar and heavy cream and bring to a boil. Boil for 4-5 minutes, stirring frequently. Remove from heat when it starts to thicken a bit. Add the vanilla and bourbon and stir. Set aside to cool. The sauce will thicken as it cools.
To make the batter, whisk together the dry ingredients. Mix the wet ingredients in a separate bowl and then add together. Mix just until combined, do not over mix. Pour batter into a greased muffin tin and bake for 12-15 minutes or until a toothpick comes out clean.
To make the frosting, add the butter to a mixer and mix until smooth. Add the vanilla and salt. Add the powdered sugar in increments altering with the heavy cream, mixing in between. (Ex. 1 cup of powdered sugar and 1 tbsp heavy cream, then mix, then repeat. Add as much powdered sugar as you like to get the consistency that you desire.
Once the cupcakes cool, frost them and drizzle with butterscotch sauce. Enjoy!