3 pounds cremini, button mushrooms, or other variety
1½ cups rice wine vinegar
½ cup apple cider vinegar
1½ cups sugar
½ cup honey
3 tablespoons Dijon mustard
3 tablespoons whole-grain mustard
1 tablespoon kosher salt
5 thyme sprigs
1 fresh bay leaf
Lightly rinse the mushrooms; do not soak them. Dry the mushrooms, cut into bite-sized pieces, and put in a glass container.
Combine all of the remaining ingredients in a small saucepan, stir well, and bring to a boil over medium-high heat.
Pour the brine over the mushrooms and cool to room temperature. Cover and refrigerate for at least 1 week before eating to allow the mushrooms to cure. The mushrooms will keep for up to 2 weeks in the refrigerator.