Preheat the oven to 350°F (175°C) and line a 12-cup muffin pan with cupcake liners.
Melt the chocolate for the cupcake batter and allow it to cool slightly.
In a bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt.
In a separate bowl, beat the softened butter and sugar until light and fluffy.
Add the vanilla and Irish cream, then mix until combined.
Add the egg whites one at a time, mixing after each addition.
Add half of the dry ingredients and half of the buttermilk. Mix gently. Add the remaining dry ingredients and buttermilk, mixing only until combined.
Divide the batter between two bowls. Stir the melted chocolate into one portion
Alternate spoonfuls of vanilla and chocolate batter in the cupcake liners, filling each about two-thirds full. Gently swirl the batters with a toothpick
Bake for 15 to 18 minutes, or until the cupcakes spring back lightly and a toothpick comes out with a few moist crumbs
Cool the cupcakes in the pan briefly, then transfer them to a wire rack and cool completely.
For the filling, combine the chopped chocolate and warm heavy cream. Let the mixture sit briefly, then stir until smooth. Add the Irish cream and mix well
Cut a small cavity from the center of each cooled cupcake and fill it with the Irish cream ganache
For the frosting, beat the softened butter until creamy. Gradually add the powdered sugar and cocoa powder.
Add the Irish cream and vanilla. Beat until fluffy, adding heavy cream a little at a time until the frosting reaches a smooth, pipeable consistency
Pipe the frosting onto the cupcakes and decorate with chocolate shavings or curls if desired
