In a small pot, combine the mustard powder, garlic powder, turmeric, and water. Whisk mixture, breaking up any lumps, until completely smooth. Bring to a simmer over medium-low heat. Cook, whisking occasionally, for 20-25 minutes, until thickened to the consistency of prepared yellow mustard. Be careful not to let mixture scorch or dry out.
2. Step
Remove the pot from the heat and stir in the vinegar and salt. Let cool completely.
3. Step
Transfer to a clean airtight container and store in the refrigerator. The mustard should keep for up to 1 year.
