Combine cauliflower, onions and salt.
Cover with ice; let stand 2 to 3 hours.
Combine vinegar, sugar, mustard seed, celery seed and turmeric in a large sauce pot.
Cut two small slits in hot red pepper.
Add pepper to vinegar mixture.
Bring to a boil.
Add cauliflower and onions; return to a boil.
Reduce heat and simmer 7 minutes.
Remove hot red pepper.
Pack hot into hot jars, leaving 1/4 -inch head space.
Remove air bubbles.
Process 10 minutes in boiling water bath.