The most successful crudites are composed of generous quantities of perfectly fresh vegetables. This dip can be prepared a day or two before serving and stored in the refrigerator in an airtight container
Prepare a large bowl of ice water, and set aside. Bring a large pot of water to a boil, and add 1 tablespoon salt. Trim beans, and place in the boiling water. Blanch until the color becomes bright green, 15 to 25 seconds. Use a slotted spoon to transfer beans to the ice bath to cool. When cool, remove them from the ice water, pat dry with a paper towel, and set aside. Trim woody ends from asparagus, and immerse in the boiling water. Blanch until bright green, about 30 seconds; transfer to the ice bath to cool. Remove them from the ice water, pat dry, and reserve.
Separate celery stalks, and wash thoroughly. Using a vegetable peeler, peel away any tough, stringy fibers from the outside of each stalk. Trim the bottoms and tops off each stalk, and set aside. Peel jicama, and cut into 1/4-inch matchsticks, measuring 3 to 5 inches in length. Set aside. Wash cucumber very well, and cut in half (if using regular cucumbers); cut cucumber into spears, and set aside. Trim scallions to 9-inch lengths, and set aside. Wash and peel carrots, and cut lengthwise into strips measuring 1/4 inch in diameter. Set aside.
Wash squash and zucchini very well, and cut into 1/16-inch-thick slices lengthwise, preferably on a mandoline. Peel daikon, and cut into 1/16-inch-thick slices lengthwise. Set aside all the slices, covered with a damp towel, until serving time. Wash and dry cherry tomatoes. Set aside.
To make dip, combine sour cream, buttermilk, pepper, chives, thyme, shallot, and remaining 1/2 teaspoon of salt in a medium bowl, and stir well to combine. Set aside
Place beans, asparagus, celery, jicama, cucumbers, and carrots in serving glasses. Roll up squash, zucchini, and daikon strips, and place on the serving platter with the other vegetables. Place tomatoes in a bowl or glass. Serve crudites with dip on the side.