Windrose Farm grows what may be America's most delicious heirloom tomatoes. A writer visits the land of Oxhearts and Zapotec Pleateds, and tracks down California's most opulent BLT.

The only way to ponder the secret of Windrose Farm is at sunset, with a glass of wine. From halfway up the dry brown hill that shadows its 71 acres, you can look down into the green valley where perfect tomatoes are born. This year, they came in well over 60 varieties.

"Bred for flavor alone," confirms Bill Spencer, who specializes in heirloom tomatoes at this farm near Paso Robles. One of the first California growers to concentrate on heirlooms and sell them directly to restaurants, he and his wife, Barbara, have been hand-delivering their crop to chefs along the coast for the past eight years.

"It's kind of a special piece of land," Bill explains. "We have a ton of topsoil for the roots to work in. And there's something about the water, because the flavor we get is absolutely unique. It's all about terroir."

Though he spent his teens less than 20 miles from Windrose and had always done some kind of farming or ranching, Bill was not the kind of guy who discussed terroir until he took up with Barbara, in 1989. A concert cellist and studio musician, she came to Paso Robles for a Mozart festival and fell in love with the land and with Bill, in that order. "Long story short, we got along, and 10 days after we met we hosted an open house for about 35 people," Bill recalls.

In the beginning, the couple planned to grow a few rose bushes and maybe a peach tree. Then a friend gave them some heirloom tomato plants to try, and they discovered the difference in flavor between a hybrid tomato, which is bred to ship, and an heirloom tomato, which is bred to eat. The Spencers realized that if they grew heirlooms—plant varieties that, unlike hybrids, pollinate themselves with the help of the wind and willing insects—and saved seed from the ones that tasted best, they'd end up with a crop that would do brilliantly at Windrose Farm, and at Windrose Farm alone.

Then, at a conference in 1992, Bill and Barbara met Los Angeles chefs Mary Sue Milliken and Susan Feniger of the TV program Too Hot Tamales, who suggested they sell tomatoes directly to restaurants. They were willing. "If you grow weird food, you need the right kind of person to buy it," Barbara recalls. "And having been a musician, I understood chefs. They work ridiculously hard, doing what they love, and there are egos. I'm also too old to be intimidated by them."

In scoping out a potential client, she'd usually eat at the restaurant alone, in jeans, leaving a basket of tomatoes for the chef's consideration. Sometimes she would be bolder. "I was working at Campanile in 1996 and Barbara came in the back door in her little overalls and straw hat and said, 'I have great tomatoes,'" Los Angeles chef Suzanne Goin remembers. "I thought, Yeah, sure you do, but then she took me out in the parking lot and opened up the back of her truck, and I just freaked out—it looked like a jewel box."

When Goin opened Lucques and then A.O.C. in L.A., the tomatoes followed her. She uses them now in everything from salads to a luxurious BLT made with toasted brioche and homemade garlic mayonnaise.

"I met Barbara in 1995, when I was working at Pinot Bistro in L.A.," recalls Christian Shaffer of Chloe in Playa Del Rey, who tosses Windrose tomatoes with olive oil and basil to pair with his delicate goat cheese panna cotta. "I had never seen an heirloom tomato per se, and there was nothing that compared. Still isn't. I pretty much think she grows the best fruit in the state of California."

The kitchen of the Spencers' house is full of that exemplary fruit—red, yellow, orange, pink, white, green, purple, even black, the tomatoes sit in bowls and on counters, ready to be tasted. "Now here's a Ruby Gold," Barbara says, bisecting a tomato streaked yellow and red. "This is what we go for," she explains. "No drips. If it drips, it won't have the intensity." While she speaks, she renders seed for next year's plants and slow-roasts tomatoes, garlic and onions to toss with pasta. The Spencers eat well.

"Black ones taste the best, red I'm not that interested in, green I have trouble taking seriously," she says. "Cherokee Purple, Oxheart, Persimmon," she continues, ticking off her list of personal favorites. "Hillbilly, Black Krim, Chianti Rose...and whatever I grow next year. One year is never anything like another."

For a trip to the Carmel restaurant Bouchée, Barbara has her crew fill boxes with the best of that day's harvest, including a monster pink Mexican variety covered with intricate folds, the Zapotec Pleated.

"The boxes are always something of a surprise," says Bouchée's chef, Walter Manzke. "You might have six Green Zebras or 20 Caro Riches, the orange ones. Low acid, very sweet. They might be my favorites."

When Manzke worked at Patina in Los Angeles, he was once asked to produce a truffle dinner and begged to do a tomato one instead. Tomatoes inspire him. Since coming to Bouchée, he's created a clear Bloody Mary in a shot glass, gelées, granitas, sorbets, salsas and barbecue sauces, and of course salads, all with Windrose tomatoes and none predictable. Tonight, he will layer slices of the tomatoes with watermelon and mozzarella, then top the salad with shards of frozen balsamic vinaigrette.

Having crammed the back of her aged Explorer with quilt-covered crates of tomatoes, Barbara begins the three-hour trip to Bouchée. By the time she gets to Carmel, she's driving through a cool fog. When she arrives, the restaurant staff is frantically preparing for the dinner rush, and only pastry chef Margarita Manzke can be spared to look at the fruit, lined up in boxes in a very narrow alley near a dumpster.

"They're so ripe," Margarita says in awe. "They glow—almost like a healthy person."

"How many do you want?" Barbara asks.

Only one answer makes sense.

"I want them all."

Robin Chotzinoff is the author of People with Dirty Hands. She lives in Colorado, where she grows tomatoes at 8,000 feet above sea level.