I just got a new propane burner and it’s leaving a lot of soot on the brew pot
what’s the best method / cleaning agent for removing the soot build up?
Barkeeper’s Friend works well. Or you can use the old Boy Scout trick of soaping the outside of the pot before you use it.
Once you’re got it off I know some folks soap the exterior of their kettles. I’d say more, but that’s all I remember. 
Also, next time check the oxygen mix if you’re getting a ton of soot. Soot is usually a by product of too little oxygen and therefore a ton of underburned fuel. You want as little orange flame as possible and as much blue.
Right. I’d be more worried about why you’re getting soot than in cleaning it off the pot. Make sure it’s getting more oxygen; check air intakes to see if there are bugs, leaves, or other cruft in there.
Thanks - for the info I’ll try the bar keepers friend
and I think I just need to dial in the the air intake as it’s new I’m still getting used to it.
Personally, I’ve taken the whole air intake/shutter off of my propane burners with good results. Us brewers usually have our adjustable regulators dialed up higher than for other applications thus needing more 02 to feed those hungry flames. I know, they’re there for a reason you may think but, if they cut into our BTU output that effects our boil time and rate then radical measures need to be taken! 
I use the soap on the outside trick in case of any soot build-up. Works great. I once had a brew session where I got a tremendous amount of build up and couldn’t get a great flame going. Turns out that my burner had sat unused in the garage for awhile. I took it apart the next day and saw a cocoon in the tube totally blocking the air flow! I learned a couple lessons- keep your burners clean and brew more…
Down where I live you have to inspect for lizards.
+1 on using Barkeeper’s Friend to get the soot off. I leave a thin layer of Dawn on the bottom of ea. of my kettles. I’ve used one for 222 batches & it looks brand new!