1/3cup any wine vinegar or balsamic vinegar, or more to taste
2 teaspoons Dijon-style mustard
Salt and freshly ground black pepper
Instructions
Put the oil, vinegar, and mustard in a small glass jar along with a pinch each of salt and pepper. (If you want to add any extra ingredients, now is the time; see the Variations.)
Screw on the top of the jar and shake until the dressing becomes thick and creamy. Taste and adjust the seasoning, adding small sprinkles of salt and pepper if you like. If you want more vinegar, add it 1 teaspoon at a time until the balance tastes right to you.
Shake the jar again and serve right away or refrigerate for up to 3 days; shake well before every use.