The other mustard recipe I made from America's Test Kitchen's Foolproof Preserving is for whole-grain mustard. My mother (Julie) was less thrilled than I, responding with a disgusted, "Why?" But I actually have several recipes in my regular rotation that ask for this (including the previously posted crab mac and cheese). I've actually had trouble finding whole-grain mustard, so I've been using stone ground, but I'll be using this from now on.
As with the Dijon, this has to soak 8-24 hours, then sit out for 1-2 days for desired spice.
YIELD: 2 1-cup jars
3/4 cup cider vinegar
1/2 cup water
1/3 cup yellow mustard seeds
1/3 cup brown mustard seeds
2 tablespoons packed light brown sugar
1 1/4 teaspoons salt
Combine vinegar, water, yellow mustard seeds, and brown mustard seeds in a bowl. Cover with plastic wrap and let sit at room temperature for at least 8 hours and up to 24 hours.
Measure out 1/2 cup vinegar-mustard seed mixture and set aside. Combine remaining vinegar-mustard seed mixture, sugar, and salt in food processor and process until coarsely ground and thickened, 1-2 minutes, scraping down bowl as needed; return to medium bowl. Stir in reserved vinegar-mustard seed mixture.
Using funnel and spoon, portion mustard into two 1-cup jars. Cover and let mustard stand at room temperature until it has reached desired spiciness, 1-2 days; mustard becomes spicier as it rests. Once desired spice level has been reached, refrigerate and serve.
Mustard can be refrigerated for up to 6 months; once refrigerated, flavor will continue to mature but will not become more spicy.