Heat the beer in a small saucepan over medium heat and let it simmer until it reduces to 1/2 cup. This will take 15 to 20 minutes and be sure to watch it so it doesn’t boil over. If it starts to bubble up, stir and remove it from the heat to let it come down.
Preheat the oven to 325 degrees F. Line a 9×5 inch loaf pan with parchment paper.
In a microwave-safe bowl, combine the butter, cocoa, sugar and chocolate. Microwave for 30 seconds, stir, then microwave for another 30 seconds. Stir until everything is melted and combined. Let it cool for a few minutes.
Stir in 4 tablespoons of the beer syrup, the egg white, vanilla and salt. Stir in the flour until fully combined.
Pour the mixture into the lined loaf pan and bake for 4o to 45 minutes. The brownies are done with the top is dry and a toothpick inserted has only a few crumbs sticking. Cool the brownies completely.
Once cool, frost and top with sprinkles if desired. Slice and serve.