broken exhaust stud removal

I have gotten two frozen and broken studs out recently and saved the original threads.
Probably done 30 of them over my lifetime, and I always do it the same way.
Using a mototool to concave the end of the stud to get a good center and just worked up in sizes until I was at the size of the hole minus the threads.
Then just slowly worked the tap in and back out a few times knocked the left over threads out.
Probably spent 30 min or less on each one, but like mentioned patience is critical (especially on your first pilot hole drill)
The closer you are to centered on that first drill will dictate how the rest of it goes, and that is why I concave dress the end of the stud with the mototool first.