Step 1

Wash and dry the jars. Wash 2 wide-mouth pint jars, lids, and rings in warm soapy water and rinse well. Set aside to dry or dry completely by hand. (Alternatively, run everything through the dishwasher.)

Step 2

Prepare the cucumbers and onion. Wash and dry the cucumbers. Thinly slice into 1/4-inch thick rounds. Halve and thinly slice the onion. Toss the cucumbers and onion together in a large bowl to evenly distribute the onion among the pickles.

Step 3

Pack the cucumbers and onion into the prepared jars. Pack the vegetables into the 2 jars, leaving a 1/2-inch of space at the top. Pack them in as tightly as you can without smashing.

Step 4

Make the brine. Place the vinegar, water, sugar, salt, and mustard seeds in a small saucepan over high heat. Bring to a boil, stirring to dissolve the salt and sugar.

Step 5

Add the brine to the jars. Pour the brine over the vegetables, filling each jar to within 1/2 inch of the top. You might not use all the brine. Gently tap the jars against the counter a few times to remove all the air bubbles. Top off with more brine if needed.

Step 6

Tightly seal the jars. Place the lids over the jars and screw on the rings until tight.

Step 7

Cool the jars, then refrigerate for 24 hours. Let the jars cool to room temperature. Store the pickles in the refrigerator. The pickles will improve with flavor as they age — try to wait at least 24 hours before using.