Preheat your oven to 350°F (175°C) and prepare a 9x13 inch baking dish by lining it with parchment paper.
In a medium saucepan, melt the butter over low heat. Once melted, remove from heat and stir in the granulated and brown sugar until well combined.
Add the eggs one at a time to the mixture, whisking vigorously after each addition until fully integrated. Then stir in the Guinness and vanilla extract.
Sift in the flour, cocoa powder, and salt and gently fold until just incorporated, being careful not to overmix.
Fold in the chocolate chips until evenly distributed throughout the batter.
Pour the batter into the prepared baking dish, spreading it out evenly with a spatula.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted in the center comes out with moist crumbs.
Allow the brownies to cool in the pan for at least 10 minutes before transferring to a wire rack to cool completely before cutting.