Step 1

Place diced celery and onion in a medium nonreactive bowl. Top with the sprig of dill and set aside.

Step 2

In a medium saucepan over medium-high heat, stir together vinegar, water, sugar, salt, and celery seed. Stir occasionally, until sugar has completely melted. Pour hot liquid over celery, onion, and dill. Let mixture cool to room temperature on the counter. Put a lid on the bowl or transfer mixture to a jar.  Refrigerate for 2 days before eating. Will keep very well for a few weeks in the refrigerator.