take it to a machine shop let them do it in the milling machine if you mess it up you will spend a lot more

Agree with this method, with one exception. Use a fender washer, weld it to the remaining stud 1st, you will get better penetration to the stud. Then weld a nut to the washer. Let it cool a bit and slowly work it out. As stated in the above posts this is one of the best and easiest methods. If you drill, use a small bit at 1st, make sure it is centered perfectly, lube the heck out of it, then slowly go bigger. After you get a good hole you can use a small carbide on a Dremel or die grinder and work the remaining stud to just about where the threads show and pick the remaining pieces out. Not the quickest method but does work as a last resort. We use to use both methods at the Cat dealer I use to manager years ago.
Pete

Sometimes if not much thread to the stud is exposed, a castle nut just a c hair bigger than the stud placed upside down over the stud will give you more surface area to weld.

Ya, tap burner. That's exactly what one needs to remove an EZ out because they're harder than whore's heart.

just used the weld on nut method on gm 6.0 aluminum heads 3 broken manifold bolts worked like a charm the heat from welding expanded the aluminum came right out.