Prepare a boiling water bath canner (or large stock pot) and at least 6 half-pint jars and lids. I usually prepare a few quarter pints as well, to hold any extra syrup that might be left over. Sterilize the jars and lids as per recommended standard USDA procedures.
Remove the stems and slice the jalapeno peppers into ¼ inch-width rounds. You can do this by hand with a sharp knife, or more quickly with a mandolin (if you have one). Due to the amount of hot peppers you are working with, I strongly recommend wearing gloves. Despite best efforts, I usually end up with jalapeno oil under my nails or in my eye, but hopefully you have far more luck than I do!
In a large non-reactive pot, combine apple cider vinegar, sugar, and spices and bring to a boil over high heat. Reduce and simmer for about 5 minutes. Add all of the pepper slices to the syrup and allow them to simmer for another 5 minutes –be careful not to over-cook, as you want the peppers to keep some of their crispness and shape. While these simmer, arrange your (still hot) sterilized jars on a clean kitchen towel on the counter nearby. Using a pair of tongs or a slotted spoon, transfer the pepper slices into the canning jars, leaving ¼ inch head-space from the top of the jar. Once all the jalapeno slices are removed, raise the heat and bring the syrup back up to a rolling boil, and allow to reduce for about 8 minutes.
Very carefully, ladle the boiling syrup into the jars of jalapeno slices, still leaving the ¼ inch head-space. Remove any air bubbles with a “bubble remover” or cooking chopstick by inserting it into each jar a few times to release any trapped air. Add more syrup if necessary. Wipe the rims of the jars with a damp paper towel so that stray syrup doesn't interfere with the sealing process, and screw the clean lids and rings on to finger-tip tightness. If you have left over syrup, ladle it into the extra sterilized jars and prepare them for processing along with the jalapeno slices.
Place the jars in the water bath canner. Bring to a full boil, then allow the jars to process for 10 minutes. Remove with a jar lifter and transfer to a folded kitchen towel on your kitchen counter. Leave them untouched for 24 hours, then check the seals, label, and store in a cool, dark place without the rings. Like most pickles, these are best eaten if you allow them to sit and cure for at least two weeks before opening. Properly sealed, jars should remain shelf stable for up to a year.