1/2cup unsalted butter(1 stick) at room temperature
2 1/2cupspowdered sugar
1 teaspoonpure vanilla extract
2-3tablespoonsIrish stoutsuch as Guinness
Place the oven rack in the center position and preheat the oven to 350 degrees F. Spray an 8x8-inch baking dish with nonstick spray. Line with parchment paper, leaving some hanging out opposite sides like handles. Spray again, then set aside.
In a large heatproof bowl set over a pan of simmering water (do not let the bottom of the bowl touch the water), melt together the chopped chocolate and butter. When the chocolate is almost melted, remove from the heat and stir until the mixture is completely melted together and smooth. Let cool 5 minutes.
In a separate bowl, sift together the whole wheat pastry flour, all-purpose flour, cocoa powder, and salt.
Once the chocolate mixture has cooled, whisk in the granulated sugar until combined. At this point, the mixture will look grainy. Stir in the eggs, one at a time, fulling combining between each addition. Keep stirring until chocolate mixture is smooth and glossy (about 40 strokes). Stir in the vanilla extract.
Add the dry ingredients to the chocolate mixture a few tablespoons at a time, stirring in between each addition, just until the flour disappears. Slowly stir in the beer. It will foam as it is added, but keep working in additions and stir until the foam subsides. Fold in the chocolate chips.
Scape the batter into the prepared pan and smooth the top. Place in the oven and bake until a toothpick inserted in the center of the brownies comes out with just a few moist crumbs clinging to it, 25 to 30 minutes. Cool to room temperature, then remove from the pan using the parchment-paper handles.
Meanwhile, prepare the Guinness frosting: In the bowl of a standing mixer fitted with the paddle attachment or a large mixing bowl, beat the butter until light and fluffy, about 1 minute. With the mixer running on low, slowly beat in the powdered sugar. Add the vanilla extract and 2 tablespoons of stout. Continue beating until the frosting is smooth and fluffy, about 3 additional minutes. If you'd like a thinner frosting, beat in 1 additional tablespoon stout. Spread over the cooled brownies. Slice and enjoy.
Store leftovers in the refrigerator for up to 5 days or freeze for up to 3 months. Let thaw overnight in the refrigerator.