Soak mustard seeds for at least 2 hours, or over night. This will give you a finer texture. This will also mellow the seeds out slightly, so feel free to add some black mustard seeds.
1/2 cup brown mustard seeds, 1/2 cup yellow mustard powder
Drain mustard seeds and then grind in a coffee grinder, food processor, mortar and pestle, or throw it all in the blender (my favorite method).
Blend soaked brown and yellow mustard seeds and add new water. Let sit for 10 minutes to allow flavors to emerge from seeds.
1/4 cup water
Add vinegar, salt, and turmeric and blend until smooth.
1/2 cup white wine vinegar, 1-1/2 teaspoon salt, 1 teaspoon ground turmeric