This is quite possibly the easiest dessert to make. Simply stir your beer and brown sugar together in a high-sided bowl and pour the mixture into an 8-inch square baking dish. Let freeze for 1 hour, until you see ice crystals forming at the edge of the baking dish.
Using a fork, mix the icy part of the granita into the rest of the beer mixture in the dish. Continue to do this every 45 minutes or so, until the dish has an Italian ice texture. This could take 3 to 4 hours.
To serve, simply scoop into a cup.