Add the beer to a pot over high heat. Reduce by half (about 3/4 cup remaining), stirring frequently. Remove from heat, and add the chocolate. Stir until smooth and melted.
Allow to cool to room temperature. Cover and refrigerate until set, about 2 hours.
Use a melon baller to scoop out a small amount of chocolate. Remove centers from freezer. Sandwich one dollop in the middle of the truffle mixture and roll into a ball with your hands. Chill for 20 minutes to an hour.
Heat chocolate in double boiler, on low. Stir until the chocolate is just melted. Remove from heat. Roll each truffle ball in melted chocolate until coated.
Place on parchment paper, sprinkle with desired topping. Chill until ready to serve.