Bring the beer and butter to a simmer in a heavy saucepan over medium heat.

Add the cocoa powder and whisk until smooth. Remove from heat and set aside.

In a large bowl, whisk together flour, sugar, baking soda, and salt.

Using an electric mixer, beat together eggs, sour cream, and chocolate mixture from step 1 & 2.

Reduce to low speed and gradually add the flour mixture. Mix until smooth.

Divide the batter into cupcake liners and bake for about 17 minutes or until a toothpick inserted into the center comes out clean. Cool cupcakes on a wire rack.

While the cupcakes are cooling, make the filling. Start by placing finely chopped bittersweet chocolate in a heat-proof bowl.

Heat heavy cream to simmering, then pour over chocolate and cover for a few minutes.

Stir in butter and whiskey until well combined. Let cool until thick but still soft.

Using a 1 inch round cookie cutter, cut out the centers of the cupcakes, saving the cut outs.

Fill the cupcakes with the Ganache filling and replace the cutouts.

Now make the frosting. To start, use the whisk attachment on the mixer to whip the butter on medium-high speed for 5 minutes.

Reduce speed to medium-low and gradually add the powdered sugar

Add the Bailey's, increase speed to medium-high and whip for another 2-3 minutes until light and fluffy.

Frost the cupcakes!