Place all of the ingredients in a small, nonreactive bowl and stir to combine. Cover tightly with plastic wrap and let sit at room temperature for at least 24 hours.
Remove the plastic wrap and transfer the mustard mixture to a blender. Blend until the desired consistency is reached, about 30 seconds for a coarse texture.
Transfer the mustard to a small, nonreactive container with a tight fitting lid, cover, and refrigerate for up to 3 months. The fresher the mustard, the spicier the taste.
