In a Large pot, place the onions, cauliflower, and cucumbers. Add the vinegar, sugar, dry mustard, turmeric, and salt. Simmer gently until tender, about 15 minutes.

Turn off the heat. In a small bowl, combine the cornstarch with about 2 tablespoons of water to make a slurry, then whisk the slurry into the vinegar mixture.

While the mixture is hot, pour it into the Mason jars, cap them, and listen for the "doink" when the cap is pulled in by the cooling of the pickles.

After about 15 minutes, test the tops with a gentle push to make sure they're sucked in. Don't worry: For any that aren't, you can refrigerate or you can reheat and re-cap.

Store your pickles in a cool, dry, dark place. [FIJ note: Please do refrigerate these jars, none of this is proper canning procedure.]