Set oven to broil or heat BBQ on high.
Trim and clean green onions.
Coat bottom of a baking pan or BBQ grill with oil. Toss green onions in oil. Season with fresh ground salt and pepper.
Grill or broil until slightly charred. This could take up to 10 minutes but watch carefully to ensure they don't burn.
When slightly charred cut them into 1" lengths.
Heat corn kernels in the microwave so they are just warm. DO NOT OVERCOOK! Add in peppers and green onion.
For the dressing add vinegar, tarragon, mustard and sugar in the blender. Add the oil in a slow but steady stream so it emulsifies to a cream dressing. Add sour cream and blend in. You will have extra dressing.
Stir a small amount of dressing into the corn mixture -just enough to coat. If you add too much dressing you will lose the fresh flavour of the corn and green onions. Reserve the remainder of the dressing for another use.
Serve slightly warm or at room temperature.