1 bunch red radishes (about 13 radishes)
1/2 cup red wine vinegar
1/4 cup granulated sugar
1/4 cup water
2 teaspoons kosher salt
1/2 teaspoon yellow or brown mustard seed
1/4 teaspoon whole caraway seeds (coriander, fennel, or cumin seeds can be substituted)
1/4 teaspoon whole black peppercorns
Remove from heat and let pickling brine cool for while you slice the radishes thinly. I put the radishes in a canning jar, but any non-reactive bowl will work. Pour brine over them. The brine didn't quite cover the radishes, so I just added a little more water. Let cool at room temperature for 20 minutes; cover and refrigerate.
The radishes were ready to eat after just an hour, but really tasted delicious the second day.