WIth the current IDE 4 steps are needed to return to an ongoing project: FIrst you must go to 'recent projects, select the one wanted. It the pops open on top of the blank starter project which needs to be then dismissed so one can continue work. Microsoft Visual Studio provides a setting to mark the currently active project and then each time VS starts it loads this project. Couldn’t Processing offer a similar feature? Does not seem like it would take any heavy programming to add it,
I don’t know of a way to set a default project in the editor.
You can open a .pde file directly. So maybe the solution is to add a shortcut to your current project to your desktop, and open Processing from that?
Awesome! Processing is open-source, so feel free to make a pull request!
Kevin - thanks for the short cut idea - works just fine. It was sorta a “duh” moment - should have thought of it! 
Alan R.