Mac tip: Menu bar on dual external monitor

I've solved a problem that's been driving me crazy for years. I always have an external monitor hooked up to my laptop when I'm working from home, and I thought it was impossible to identify the external monitor as the primary screen while keeping the laptop display active. Using two screens was no problem, but the primary screen always had to be the laptop display. No longer!

Go to System Preferences
Click "Displays"
Select the "Arrangement" tab
Drag the menu bar from one screen to the other (see the screen grab below)