Slice the cucumbers into thin rounds (about 1/8-inch thick) using a sharp knife or mandolin slicer.
If using, thinly slice the onion as well.
2. Make the Brine:
In a medium saucepan, combine the vinegar, sugar, water, salt, mustard seeds, celery seeds, turmeric, red pepper flakes (if using), and smashed garlic (if using).
Bring the mixture to a simmer over medium heat, stirring occasionally until the sugar and salt have dissolved. Once the brine is hot and the sugar has dissolved, remove the pan from the heat.
3. Pack the Jar:
In a large mason jar or other airtight container, layer the sliced cucumbers and onion (if using).
Pack them tightly, but leave some space at the top to ensure the brine covers all the vegetables.
4. Pour the Brine Over the Vegetables:
Pour the hot brine over the cucumbers and onions, making sure they are fully submerged. If needed, use a spoon or knife to gently press the cucumbers down to ensure they are covered with brine.
5. Cool and Refrigerate:
Allow the jar to cool to room temperature.
Once cooled, seal the jar with a lid and place it in the refrigerator.
Let the pickles sit in the fridge for at least 24 hours to allow the flavors to meld. The pickles will taste even better after a few days.
6. Serve:
After 24 hours, your refrigerator bread and butter pickles are ready to enjoy! They will last in the refrigerator for up to 2-3 weeks.
