1 tablespoon sherry vinegar, white wine vinegar, or fresh lemon juice
Instructions
To make by hand: Put the yolk and mustard in a medium bowl. Beat together with a whisk. Begin to add the oil in dribbles as you beat, adding more as each amount is incorporated. You’ll notice when a thick emulsion forms. Then you can add the remaining oil a little faster. Depending on how fast you beat, the whole process will take about 5 minutes. To make by machine: Put the yolk and mustard in a blender or food processor and turn the machine on. While it’s running, add the oil in a slow, steady stream. When an emulsion forms, you can add it a little faster (and scrape down the sides as necessary), until all the oil is incorporated.
Stir in the pickles or capers by hand. Add salt and pepper, then stir in the vinegar. Taste and adjust the seasoning. Use immediately.