Yes, it's called "clamshell mode." To use this operation you close your PB, connect your monitor to your PB, connect your external keyboard and mouse and click or tap a key. Your external should start right up while your PB screen will stay off untill you click detect display from your system preferences to start "screen spanning mode."
You should run a search next time around, this has been discussed time and time again along with other normal usage questions.