I noticed one of my torsion bar adjusting nuts is snapped off at the base of the adjuster. How could I get the nut removed?

pretty sure the come as a set. the bar and the bolt. so unless you just have a lone bolt handy, I wouldn't worry about it.

So it broke at some point, not when you were adjusting it?

An easy out extractor should work really well on that since it's likely not stuck. Just get the weight off the tires and start in on it. Get some penetrating oil on there the day before just in case.

The bolts are available seperately when you are ready to put a new one in.

Not an easy out unless the bolt is broke flush.Use a stud remover.I have 2 sets metric and standard.They look like deep well sockets and can grab the stud if it sticking out.Like said take the load off the wheel.I doubt you can drill the bolt they are hard.Rocky

I have seen this up close on my own car! I welded a round/tubular piece of metal to the remaining stub, then used a pipe wrench to back out the darn thing