1 pound turnips, peeled and sliced paper thin
2 (4-inch-by-2-1/2-inch) pieces kombu
1 cup rice vinegar
1 cup granulated sugar
1 cup water
2 tablespoons kosher salt
Place the turnips and kombu in a 1-quart jar, leaving at least 1/2 inch of room at the top of the jar.
Make the brine: Place the vinegar, sugar, water, and salt in a small saucepan, whisk to dissolve the sugar and salt, and bring to a rapid simmer.
Immediately pour the brine over the turnips, making sure to cover them completely but leaving 1/4 inch of room at the top of the jar. Let cool to room temperature, about 1 hour.
Cover the jar with a tightfitting lid. Shake the jar or turn it upside down to evenly distribute the brine, then place it in the refrigerator for at least 1 day and preferably 1 week before using. (The pickled turnips can be kept in the refrigerator for up to 2 months.)