In microwavable bowl, microwave frosting uncovered on High 10 to 30 seconds or just until melted and spoonable, but still thick. DO NOT BOIL. Carefully spoon melted frosting over brownies to glaze, allowing excess to drip down sides. Sprinkle with candy sprinkles before frosting sets. Allow frosting to set, about 2 hours. Store covered in a single layer at room temperature.