So what method do you use now?
Off the top of my head...
-route the outer edge to a uniform final depth
-if the pickup plane is to remain flat, mark off that area
-doodle some topographic lines as required
-hog off the bulk with a grinder
-switch to chisels, planes, scrapers... you name it
-fine tune with sandpaper
I haven't done a tutorial in a while, but Jason Schroeder shows you exactly what I'm talking about in these photos...