I have had good luck welding a thick washer to a broken off bolt, then weld a nut to the washer and use the nut to turn out the offending member.

I think this works better because it is easier to get better penetration into the bolt using a washer rather than trying to weld down inside a nut.

Remember 9-11-01--God Bless the USA
JUSTICE, not REVENGE, will prevail

1951 Chevy 1/2-ton Pickup truck