Slice the cucumbers into thin coins, about an eighth of an inch thick. Slice the onion into thin half-rings. Put both into a colander set over the sink or over a bowl.

Sprinkle one teaspoon of kosher salt over the cucumbers and onion and toss everything together with your hands. Let the mixture sit in the colander for thirty minutes. You will see quite a bit of water drip out. This is important. Press the cucumbers gently with your palm at the end to squeeze out more liquid, then pat dry with a paper towel.

While the cucumbers drain, make the brine. In a bowl or large measuring cup, whisk together the apple cider vinegar, cold water, sugar, celery seed, turmeric, remaining salt, and black pepper. Whisk until the sugar is fully dissolved and the brine looks a uniform pale yellow color. Taste it. It should be noticeably sweet with a tangy edge.

Pack the drained cucumbers and onion into a quart jar or airtight container. Pour the cold brine over the top. Use a spoon to press the cucumbers down so the brine covers as much of the surface as possible. Seal the container.

Refrigerate for at least four hours before serving. Overnight is better. When you open the jar, the brine will have turned a soft golden color from the turmeric and the onion will smell sweet and mellow rather than sharp.

Serve cold as a side salad or pile onto sandwiches and pulled pork. Give the jar a gentle shake or stir before each use to redistribute the brine and spices.