Store-bought “prepared” yellow mustard is a staple in most households, but with just a little planning, you can make your own mustard using ingredients that you probably already have on hand. This spicy version is great for dipping soft pretzels into or smearing on a grilled cheeseburger.
Allyl isothiocyanate, the oil in mustard seeds that gives pungency and heat, tends to dissipate over time, so the longer the mustard sits in the refrigerator, the less spicy it will become.
Place the ground mustard, sugar, and salt in a medium heatproof, nonreactive bowl and whisk to combine. Add the egg and whisk until smooth. Add the vinegar, paprika, and turmeric and whisk until combined. Cover the bowl tightly with plastic wrap and refrigerate for 2 hours.
Fill a medium saucepan with 1 inch of water and bring it to a bare simmer over low heat. Remove the plastic wrap from the mustard mixture, place the bowl over the simmering water, and cook, whisking constantly, until the mustard mixture has thickened to the consistency of olive oil, about 8 to 10 minutes. (Check to make sure the water isn’t boiling by periodically removing the bowl from the saucepan using a potholder or dry towel. If the water is boiling, reduce the heat so the egg doesn’t curdle.)
Transfer the mustard to a nonreactive container with a tightfitting lid and cool completely. Seal the container and refrigerate for up to 2 weeks.