Whole-Grain Mustard Burgers

The mustard seeds in these hearty, pungent burgers are soaked in balsamic vinegar, which softens their skins, giving them a resiliency that makes them pop between the teeth with every bite. The horseradish in the mixture underscores the mustard flavor, and the concentrated sugars in the balsamic vinegar naturally counter the slightly bitter aftertaste of the mustard seed. See the sidebar for more information on mustard.