Set out a large mixing bowl and a mandolin slicer if you have one. Slice the pickles into even 1/8 inch rounds. Then quarter and slice the onion into short segments.
Place the cucumber slices and onions in the bowl, and toss with kosher salt. Set in the fridge to rest for 1-3 hours.
Meanwhile, set out for clean pint jars. Divide the mustard seeds, crushed red pepper, celery seeds, and cinnamon sticks between the four jars.
Once the cucumber slices I’ve had plenty of time to rest, release their juices, and absorb the salt, rinse them in cold water to remove the excess salt. Divide the cucumber slices and onions between the four jars.
Set a small saucepot over high heat. Add the sugar, apple cider vinegar, white vinegar, and turmeric. Bring to a boil.
Once boiling, carefully ladle the hot pickling liquid into the jars, dividing it evenly. If some of the cucumbers are still sticking out of the top of the jar, uncovered, add a tablespoon or two of hot water to the jars. Screw the lids on tight and shake the pickle jars.
If planning to make as refrigerator pickles, let the pickles sit at room temperature for one hour, then moved to the refrigerator. If planning to can the pickles, follow proper canning procedure at this point.
Let the pickles rest at least 48 hours before eating. The texture and flavor will improve over the next week.
Refrigerator pickles should last at least two months if kept cold. Canning pickles can last 1-2 years if sealed properly.