Combine 2 tablespoons vinegar, ¼ teaspoon mustard and ⅛ teaspoon salt in a bowl; whisk until dissolved.
Whisk in 6 tablespoons oil, 1½ teaspoons shallot (or scallions and/or ¼ teaspoon herbs) and a big pinch of pepper.
Alternatively, combine all ingredients in a screw-top jar; cover and shake vigorously for 30 seconds to blend thoroughly.
Taste carefully and adjust seasoning as desired.
