Arrange 15 rinsed nasturtium leaves around the outside edge of a large flat plate. Lay 15 clean nasturtium flowers on top of the leaves, with the stems pointing to the center of the dish.
Working toward the center of the plate, next add a layer of finely sliced sweet onions, then a layer of finely sliced tomatoes and a layer of chopped celery. Continue layering with onion, tomato and celery until the dish is full. Sprinkle 1/2 cup of vinaigrette dressing over the salad and garnish with chopped hard-boied egg. Garnish with borage flowers.
Cover and refrigerate for several hours before serving.