5 lb. green tomatoes
2 medium onions
1/3 cup pickling salt or kosher salt
3 cups cider vinegar
1 3/4 cups sugar
1 tsp  ground turmeric
1 tsp  celery seeds
1 Tbsp mustard seeds

Optional – Red bell pepper or hot red pepper, cut into thin strips

Slice off the ends of tomatoes and discard. Cut tomatoes into wedges
and put into a large nonreactive pot or bowl. Peel onions then cut in
half and cut into 1/4-inch slices. Put into the pot with the wedged
tomatoes. Sprinkle the salt over the vegetables and gently toss to
coat well. Cover with a few cups of ice cubes; cover and let stand for
4 hours or refrigerate overnight.
Drain the vegetables in a large colander and lightly rinse.

In a large nonreactive kettle, combine the vinegar, sugar, turmeric,
celery seeds and mustard seeds; bring to a boil. Lower heat to medium
and add the drained tomatoes and onions to the pot. Continue to cook,
stirring gently occasionally, until the mixture is boiling. Fill with
the remaining liquid, leaving a 1/2-inch headspace.

With a clean damp cloth, wipe the rims of the jars. Place the flat
lids on the jars then close the caps with screw-on rings tightly, but
do not over-tighten.

Arrange the filled jars in the canner and add more water, as needed,
to be at least 1 inch above the jars. Bring to a full boil. Cover and
continue to boil for 10 more minutes.

These are so good we decided to make more batches.