Wash the cucumbers thoroughly and slice them into ¼-inch rounds. For the classic bread and butter pickle appearance, use a crinkle cutter if available. Place cucumber slices in a large bowl with the thinly sliced onions.
Sprinkle the kosher salt over the cucumber and onion mixture, toss well to coat evenly, and let stand for 1-2 hours. This critical step draws out excess moisture, ensuring your homemade pickles maintain their signature crunch.
Thoroughly rinse the cucumber and onion mixture under cold water to remove excess salt. Drain well, pressing out additional liquid with paper towels or a clean kitchen cloth.
In a large nonreactive pot, combine the sugar, apple cider vinegar, white vinegar, mustard seeds, celery seeds, turmeric, cloves, and ginger (if using). Bring the mixture to a boil over medium-high heat, stirring occasionally to dissolve the sugar completely.
Add the drained cucumber and onion mixture to the boiling brine. Return to a simmer, then remove from heat immediately.
Using a slotted spoon, transfer the pickles and onions into clean, sterilized jars, leaving ½-inch headspace. Pour the hot brine over the vegetables, ensuring they're completely covered while maintaining the headspace.
For refrigerator pickles: Seal jars and refrigerate for at least 24 hours before eating. These will keep for up to 3 months.For shelf-stable pickles: Process in a water bath for 10 minutes, following standard canning protocols. These will keep for up to a year on the shelf.