Coarsely grind the mustard seed. Transfer to a small bowl, add all the remaining ingredients, and mix thoroughly with a fork. Cover with plastic wrap and set aside for 2 hours. The mustard should be ready to use immediately, with a refrigerator shelf life of 3 months.
Ingredients
3 tablespoons yellow mustard seed
1 tablespoon white wine vinegar
1 1/2 tablespoons water
1/4 teaspoon salt
1/4 teaspoon freshly ground black pepper