Make a bed of the watercress on a salad plate. Toss the potato and celery with a little of the vinaigrette and place on the watercress. Strew the pear slices over top. Drizzle with the rest of the vinaigrette and sprinkle with the walnuts. You may add a few chunks of crumbled Gorgonzola as well.
To make Gorgonzola Cream Vinaigrette, place all the ingredients in a food processor and pulse quickly just until combined. Do not overprocess.