This less an actual recipe than a logical thought progression. It blew up on the internet a couple of months ago and we finally almost emptied a mustard to give it a try. Your jar needs to have a tight-fitting lid because you just shake it up in there. And it calls for Dijon mustard, but you can probably use whatever’s on hand – just adjust salt and sugar accordingly.
1 T Dijon mustard, in its jar
1/4 c white or red wine vinegar
3/4 c olive oil
1/2 t sugar
1/2 t salt
pinch ground black pepper
Put all ingredients in jar, screw on lid and shake until emulsified. Taste and adjust spices.
Here’s an example of how to adjust the method: we had honey Dijon, so I omitted the sugar. I also used sherry vinegar. Other good herbs with mustard include tarragon or rosemary.