Preheat oven to 325 degrees and spray an 8x8 pan with nonstick spray. Whisk eggs in a medium bowl, add Guinness Stout, oil and water, then blend until well incorporated. Pour into pan and spread evenly.
Bake for 19-22 minutes or until a toothpick inserted in the center comes out clean. Cool completely on a wire rack.
To make ganache, place chocolate chips, Guinness and butter into a microwave safe bowl. Heat in 30 second increments until chocolate begins to melt, then whisk in glaze mix and stir until smooth.
Pour mixture over brownies and spread evenly. Sprinkle with cocoa powder to garnish. Freeze 5 minutes to set glaze, then cut into 9 brownies.