When I was first getting into cars, I had the privilege of being able to watch a very talented engine builder (V8s) who was very skilled at drilling out broken bolts. Back then, I had visited him a few times for those. He always let me come 'behind the counter' and see him work. He would use a hand drill and carefully get the beginning of the hole perfectly centered and then proceed to drill the whole thing out. He was always drilling for a thread insert, but he always got it straight and correctly aligned.
I think that having seen people like him work has really set my expectations for myself high. It's not every time that a broken bolt comes out this beautifully, but I think I can say that I've matched the skill of my 'mentor'. I'm very proud of myself for drilling out this broken bolt without disturbing the original threads at all. The threads in the case are not a new insert. Those are original german threads.
The circular bits on the floor are the threads of the broken bolt, which I used a 'dental pick' and tap to remove.