Always a sucker for mustard seeds, I've never seen a recipe that calls for soaking them overnight. I loved the resulting texture (other recipes I've played with call for boiling or frying the seeds). I halved Chef Matt's recipe and substituted horseradish powder for the dry mustard.
Adapted from Chef Matt Morgan
Makes about 1 cup
1/4 c. mustard seeds
1/2 c. water
1 c. chopped rhubarb
1/4 c. granulated sugar
2 to 3 teaspoons horseradish powder (Penzey's)
2 teaspoons water
Put mustard seeds in a medium bowl. Stir in 1/2 cup water; cover and refrigerate overnight.
The next day, preheat oven to 350 degrees F. Line a baking sheet with parchment paper.
Drain mustard seeds and set aside.
In a large bowl, toss rhubarb and sugar together, then spread onto prepared baking sheet. Bake for 25 minutes or until sugar has melted and rhubarb is tender.
In another large bowl, whisk together dry mustard and water. Stir in the rhubarb, then the mustard seeds. Cool to room temperature and serve, or cover and chill. Can be kept refrigerated for up to two weeks.