Using a sharp knife or a mandoline thinly sliced the red onion. The thinner the onion slices the quicker the onions will pickle! Transfer onions to a bowl or jar with enough room for the onions to be submerged once the pickling liquid is added.
In a glass measuring cup or bowl mix together the red wine vinegar, water, and kosher salt until the salt is dissolved.
Pour the pickling liquid over the sliced onion and use a fork or spoon to press the red onion under the liquid so they’re completely submerged. If they’re not quite submerged add an additional splash or two or red wine vinegar until just barely covered with the pickled liquid. As they pickled the onions will also release some liquid which will result in an increase in pickling liquid as they sit.
Transfer to the refrigerator for at least 30 minutes or up to overnight before using. The longer the onions sit in the pickling liquid the more 'pickled' they will be. When they’re ready they will appear slightly translucent and have a bright jewel toned pink hue.
