How to Make It
In a small saucepan, combine the rice vinegar with the water and sugar and bring just to a boil. Add the onion and let cool completely, about 1 hour. Drain.
In a large bowl, whisk both oils with the cider vinegar and mustard. Stir in the 1 tablespoon of crushed pistachios and the chives, then season with salt and pepper.
Using a sharp knife, remove the skin and bitter white pith from the grapefruit. Cut in between the membranes to release the grapefruit sections into the large bowl. Add the endives, parsley, tarragon and 1/2 cup of the pickled onion and toss well. (Reserve the remaining pickled onion for another use.) Season the salad with salt and pepper. Pile the salad on plates, garnish with crushed pistachios and serve right away.