Keith Dresser, America's Test Kitchen
Makes about 2 cups
Ingredients
½ cup apple cider vinegar
¼ cup yellow mustard seeds
¼ cup brown mustard seeds
¼ cup beer or water
2 teaspoons light brown sugar
¾ teaspoon salt
Method
Combine vinegar, mustard seeds, and beer in medium bowl.
Cover with plastic wrap and let stand at room temperature for at least 8 hours and up to 2 days.
Process soaked mustard seeds with sugar and salt in food processor until coarsely ground and thickened, about 1 minute, scraping down bowl as necessary.
Transfer mustard to container and let stand at room temperature until it achieves desired spiciness, then refrigerate for up to 2 months.