The bolt broke when you where wrenching it not as a result of the pot hole damage? Assuming so, that means the bond between the treading is going to make it difficult. Without something to weld to that's out.

The process would be to start drilling with a small bit as perfectly centered as possible, keeping the hole centered drill it successively larger, depending on the diameter of the bolt you'll want to get the hole large enough to tap and take the largest left hand thread bolt you can. Get it drilled, then get it tapped, run the bolt into the hole you tapped so you know it will go and how far it will go. Get some fire or heat on the drilled broken bolt, I think the chassis is a tubular threaded post, right? Get some heat on that as well. let it soak a minute and then thread the bolt in run it home and hopefully the heat will have helped brake the bonded threading and with the left hand thread bolt you'll be able to apply enough torque it beck it out. It will cool and tighten up so you might need to apply some heat as you coax it out.

If you can rig some sort of device to center the drilling that would be good, if not start with an automatic center punch, that will allow you to get as close to center as possible, then you can make a good centered mark deeper with a pointed punch and hammer. Try to keep the drill bit as straight and square as possible, use some lube, tapping fluid or wd40 to help the cutting. If you can get to a real hardware store or maybe online look for good drills, American made, expect to pay at least a couple buck each for them, you'll probably need to go online to find a correct left hand bolt and tap. Using any type of EZ-Out is a last resort, Id rather deconstruct the bolt from the inside and pick the threads out rather than take the risk of breaking off a hardened steel tool tip down in the hole(or up in the hole in your case!) Your probably going to need the correct tap for that bolt's threading to chase it before you try to thread a new bolt into place anyway so you probably should start chasing that down too. If you don't between the threadlock and any thread damage you might not be able to get the bolt fully snugged into place. Good luck

I saw this happen to someone else doing this work where they got under the car and being in an upside down orientation they tried to bust the bolt loose in the wrong direction and it just tightened a bit and snapped off when they put their muscle to it.

Chinese "cobalt "drills would be better than the average drill bit, but when they can't grind them straight and precise hardening them will only make them easier to break when they get used.