Refrigerator Bread and Butter Pickles

Bahan-bahan (3 porsi)

• 7 pickling cucumbers
• 1 white onion
• 3 tablespoons kosher salt
• 1 cup light brown sugar
• 1 cup white vinegar
• ½ cup apple cider vinegar
• 2 teaspoons celery seed
• 2 teaspoons mustard seeds
• ½ teaspoon red pepper flakes (optional)