Walnuts have been prized since ancient times, planted in groves by decree of King Solomon, and later in the Hanging Gardens of Babylon. With uses recorded in history dating to 7000 B.C.E., they are the oldest edible tree crop known to man.

The rich nuts are a mainstay of modern American baking and candy production, but they were not introduced to North America until the early 19th Century, when Spanish missionaries found the California climate suitable. Now 99 percent of U.S. walnuts are grown in California.

Most walnuts are of the Persian variety, with relatively thin shells and large nutmeats. Black walnuts are also edible but much harder to shell, and are not widely available.

Walnuts are used extensively in Persian and Greek cuisine, in desserts and savory dishes alike. English cooks make walnut pie, and Italians use walnuts to make liqueurs and pasta sauces. Americans love walnuts in cookies, fudge, cakes and otehr baked treats.

Stay chilly: If possible, store shelled walnuts in the refrigerator or freezer. Because of their high fat content, walnuts can turn rancid if left in warm conditions for several months.

Celestial snack: In Roman mythology, the gods helped themselves to walnuts, leaving acorns and chestnuts to lowly humans. No wonder mortal Romans were so happy to get their hands on the nuts, with Roman grooms throwing walnuts to wedding guests as good luck tokens.

Here, walnuts are toasted to enhance their flavor and used as the base of a chunky pesto-like drizzling sauce for grilled vegetables. The recipe is by Grace Parisi for Food & Wine. Use whatever vegetables you like to grill.

> Grilled Vegetables with Walnut Dressing

2 zucchini, sliced diagonally 1/3 inch thick

1/2 pound shiitake mushrooms, stemmed

1 red bell pepper, seeded and sliced

1 sweet onion, sliced 1/3 inch thick

1/2 cup extra-virgin olive oil, plus more for brushing

Salt and freshly ground black pepper

1 cup walnuts

1 small shallot, very finely chopped

1 teaspoon thyme leaves

1 tablespoon freshly squeezed lemon juice, or more to taste

1/2 teaspoon finely grated lemon zest

Preheat oven to 350 degrees. Light a grill. Brush the zucchini, mushrooms, pepper and onion with olive oil and season with salt and pepper. Grill the vegetables over high heat, turning occasionally, until lightly charred in spots and tender, 15 to 18 minutes. Transfer the grilled vegetables to a serving platter.

Meanwhile, spread the walnuts in a pie plate and toast for about 12 minutes, until fragrant. Let cool completely.

Transfer the toasted walnuts to a food processor. Add the shallot, thyme, lemon juice, lemon zest and the 1/2 cup of olive oil and pulse until the nuts are coarsely chopped. Season the dressing with salt and pepper and drizzle over the grilled vegetables. Serve.