Place mustard seeds, garlic and ginger in a bowl or jar and cover with the vinegar. Let stand for 24 hours at room temperature.
Place vinegar mixture in blender, add cayenne, salt, turmeric and sugar and blend until a creamy consistency is reached. You can add a bit more vinegar if it is too dry.
Once you have blended it ladle into jars leaving 1/2" headspace and water bath for 15 minutes.
Wait 3 days before using your first jar.
Notes
Adapted from Homemade Mustards - Martha Stewart Recipes