In a medium saucepan over medium-high heat, reduce Guinness and brown sugar, stirring occassionally, until thick and syrupy. Should measure to 1/3 cup. Set aside to cool.

In medium bowl, whisk together flour, cocoa, espresso powder, baking powder, baking soda, and salt. Set aside

In mixer bowl with paddle attachment, cream together butter and sugars until light and fluffy, about 3 minutes. Add eggs and yolk, one at a time, until combined. Add Vanilla extract. With mixer on low, gradually add cooled beer syrup, mixing until combined. Then gradually add step 02's mixture until no flour is visible. Fold in chocolate chips.

cool the dough for at least three hours in the fridge.

preheat the oven to 325°F. Line a large baking sheet with parchment paper. Scoop out 2 tablespoon portions 3 inches apart. Bake for about 15-17 minutes until edges are set.