Line 18 regular-sized muffin cups with paper liners.

In a large bowl, combine cake mix, Guinness, oil, and eggs, whisking til blended.

Fill muffins cups 1/2 full with batter.

Bake at 350 degrees for 15-20 minutes, or until a toothpick inserted near the center comes out clean.

Cool in the pan for 10 minutes before removing to wire racks to cool completely.

In a medium microwave-safe bowl, combine chocolate chips, heavy cream, and butter.

Microwave on high for 1-2 minutes, or until heavy cream just begins to boil.

Whisk until the chocolate and butter are completed melted, and the mixture is smooth.

Place in the refrigerator for 10-15 minutes to allow it to thicken.

Using a spoon or cookie scoop, scoop a 1-inch ball out of the center of each cupcake.

Spoon a rounded teaspoonful of ganache into the center of the hole of each cupcake.

In a large mixing bowl, beat shortening and butter until smooth.

Add powdered sugar, cocoa, vanilla, and Bailey's, beating until light and fluffy, adding additional Bailey's as needed for a thick and fluffy frosting consistency.

Frost cupcakes.