In 1-quart saucepan, heat condensed milk and fudge topping over medium-low heat about 5 minutes, stirring constantly, until hot (mixture must be hot). Cool brownies 5 minutes; poke several times with long-tined fork, wiping fork with paper towel if necessary. Pour hot fudge mixture over brownies. Cool 35 minutes before serving. Serve warm with whipped topping.