Rinse the pickling cucumbers thoroughly and slice them into ¼-inch thick rounds, then thinly slice the onion. Combine them with pickling salt in a mixing bowl.

Cover the mixture with ice and refrigerate for about 4 hours.

After chilling, drain and rinse cucumbers and onions twice under cold water.

Prepare the brine by combining white vinegar, apple cider vinegar, sugar, and pickling spices in a saucepan and heat until the mixture boils.

Add drained cucumbers and onions to the boiling brine and stir to coat.

Pack the cucumber and onion mixture into sterilized jars, leaving 1 inch of headspace.

Pour the hot brine over the packed ingredients and seal the jars tightly.

Process the jars in a boiling water bath for 15 minutes.

Let jars cool at room temperature before storing in a cool, dark place or refrigerating.