Make cupcakes: Preheat oven to 350° and line a muffin tin with cupcake liners. In a large bowl, combine cake mix with vegetable oil, eggs, and ¾ cup Baileys. Bake according to package directions and let cool completely before frosting.
Meanwhile, make frosting: In a large bowl, combine butter, half of the powdered sugar, ½ cup Baileys, cocoa powder, vanilla, and salt. Using a hand mixer, beat until smooth. Add the rest of the powdered sugar and beat until fluffy.
Pipe onto cupcakes and garnish with chocolate sauce and shaved chocolate. Serve.
