In large bowl, whisk together beer and cocoa powder until blended and smooth. Whisk in sugar, butter, vanilla extract and eggs, one at a time. Blend well.
Add flour and salt; whisk until batter is smooth. Stir in chocolate chips. Spread mixture in prepared pan, leveling surface with a spatula.
Bake 42 to 45 minutes in preheated oven, until top is shiny and dry, and a wooden pick inserted in the center comes out with a few moist crumbs attached. Remove from oven and let cool completely in pan on rack.