"I have read recipes where people can plain onions chopped up for 40 minutes."

From safe and approved sources?

Purees have some real safety limitations for canning. Most any low-acid vegetables - like onions - are pretty much limited to freezing, drying or pickling. Otherwise they have to be pressure canned.

The general recommendation is to can them per the approved instructions and then puree AFTER opening the jars.

Dave

Thank you Dave. So happy to see you here...as if you havent helped me enough in gardening already. Is there anything you cant do? :) . I seriously hope one day I can help someone the way you've helped me

I dont suppose theres a place or way I can safely test my own recipes is there? In regards to this thread, All I wanted to do was can 1/2 cup of pureed cooked onions, so about 2 medium onions, with about 1-2 TBS of white vinegar and 1 and a half tsp of lemon juice and no extra water . I figured there would be so acidity in there that I could easily do it in a pressure canner but obviously since its not an "approved" recipe, I know one would be skeptical about encouraging it