Pour the Guinness beer in a small saucepan and simmer over medium-low heat, stirring often, until it has reduced down to approximately ½ cup. (approx. 15 minutes) Watch it carefully so it's doesn't bowl over.

Set the syrup aside to cool completely before continuing.

Preheat the oven to 350° F and line 12 cup muffin tin with paper liners.

In a large mixing bowl, add the oil, milk, eggs, and vanilla and whisk together well.

Then add ¼ cup of the cooled Guinness reduction from step 1.

Then add in the sugar and stir to throughly combine.

Next, add in the flour, cocoa, and baking powder and whisk just until there are no clumps (careful not to over-mix)

Pour the batter equally between the cupcake tins, filling each about ¾ of the way full.

Bake for 16-18 minutes or until a toothpick inserted into the center comes out clean.

Remove the cupcakes to a wire rack and cool completely before icing.

This would be a good time to melt the chocolate chips for the frosting so it has time to cool.

Add the softened butter and melted chocolate to the bowl of a stand mixer fitted with the paddle attachment. Beat for one minute on medium speed until combined.

Reduce the mixer to low speed and gradually add the powdered sugar, scraping down the sides of the bowl as you go.

Add the 2 tablespoons of Guinness reduction and the vanilla extract.

Increase the the speed to medium-high speed and beat for about 2 minutes until the frosting becomes fluffy.

Transfer the frosting to a piping bag fitted with the tip of your choice and use a knife to frost them.

Garnish with shaved chocolate or chocolate sprinkles.