2 pounds firm zucchini
2 small onions
¼ cup pickling salt
2 cups white sugar
1 teaspoon celery salt
1 teaspoon turmeric
2 teaspoons mustard seed
3 cups cider vinegar (4% to 6% acid strength)
Wash zucchini and cut in thin slices. Peel and cut onions in quarters, then slice very thing. Add to zucchini. Cover zucchini and onions with about an inch of water and add salt.
Let stand 2 hours. Drain thoroughly. Bring remaining ingredients to a boil. Pour over zucchini and onions. Let stand for 2 hours. Bring all ingredients to a boil and heat 5 minutes.
Pack into preheated jars. Leave 1/8” headspace. Adjust caps and process in water bath canner at simmering temperature for 15 minutes. Cool. Test for seal. Store