In a smaller bowl, first whisk together mustard, balsamic vinegar and a pinch of salt. Then add the olive oil and yogurt and mix it all in. Give it a little taste and adjust salt.
1 teaspoon wholegrain mustard, salt to taste, 1 tablespoon balsamic vinegar, 2 tablespoon extra virgin olive oil, ⅓ cup plain unsweetened yogurt of choice