Cut room temperature butter into large chunks and place into a mixing bowl. Add sugar and brown sugar. Using electric hand mixers or a stand mixer, mix until creamed. Add egg and vanilla extract and mix until fluffy and mixed through. Set aside.
In another mixing bowl, combine flour, cocoa powder, baking powder, and salt. Mix. Add to butter mixture and allow to mix until it gathers into a ball. If the dough is too crumbly, add 1/4 cup of water at a time until it comes together.
With clean hands, knead well until soft and form into a disc. Wrap with saran wrap and chill in your fridge for about 15 minutes.
Meanwhile, prepare your ganache filing by adding your chopped chocolate into a heat-safe bowl.
In a small saucepan, add the cream and Guinness and bring to a boil. Pour boiling mixture over the chocolate.
Stir the chocolate until well mixed and add the butter. Stir again until butter is melted and mixed in.
Preheat your oven to 350 degrees. Grease two baking sheets.
Remove dough from fridge and seperate into quarters.
Place dough between two sheets of parchament and with a rolling pin, roll out until about 1/8 inch thick.
With a small round cookie cutter, cut as many circles as possible out of each quarter dough ball. Line the circles up on your baking sheets.
After all your circles are complete, spoon a small (about 1/2 teaspoon) dollop of ganache into the center of each and fold each circle into little triangles.
Pinch all the corners of your triangles to ensure they are tight, then move to the oven to bake for about 10-12 minutes.
Remove the sheets from the oven when done, and move the cookies to a wire rack to cool.
Store at room temperature for 3-5 days or wrap tightly and freeze for up to 3 months.