Cut potatoes into halves or quarters. Boil until fork tender, do not overcook. Drain and cool slightly.
In a tall beaker, combine parsley, dill, chives or green onions, oil, lemon juice, lemon zest, garlic, mustard, sugar, salt, and pepper. Blend with an immersion blender until well mixed, with some herbs still visible. Taste and adjust sugar, salt, and pepper.
Toss warm potatoes with half the dressing. Add more a little at a time until as saucy as you prefer. Keep extra dressing in fridge for 3-5 days (try it for pasta or grain salad too!). Serve warm or cold.
