Put aside that titillating vampire lit. Author Beverly Lewis has come up with a new magic formula for producing best-selling romance novels: humility, plainness and no sex. Lewis’ G-rated books, set among the Old Order Amish in Lancaster County, Pennsylvania, have sold more than 12 million copies, as bodice rippers make room for “bonnet books,” chaste romances that chronicle the lives and loves of America’s Amish.

Lewis has just published a new novel, The Secret, set in the idyllic village of Bird-in-Hand, which debuts on the New York Times paperback best-seller list April 19 at No. 10. Spurred by her success — and that of best-selling authors Cindy Woodsmall and Wanda Brunstetter (whose new book, A Cousin’s Promise, is set among the Amish in Indiana) — more than a dozen other Christian-romance novelists are eschewing Sex and the City-type story lines for horse-and-buggy piety. “There still isn’t enough inventory,” marvels Avon Inspire’s Cynthia DiTiberio, who edits Shelley Shepard Gray, a recent entrant to this genre. And there’s no shortage of demand: romance fiction, of which Amish-themed novels command a growing share, generates nearly $1.4 billion in sales each year, and that number is rising. (See the top 10 fiction books of 2008.)

Readers come away from bonnet books with an easy-to-digest history lesson and, jah, a little Pennsylvania Dutch dialect. There are occasional strident notes — a character or two who sound as if they’d be more at home at a Starbucks than at a Singing. But at their best, these books capture the quiet faith that suffuses Amish life. Which is not to say the Amish don’t ever have fun. Most of the books are set during the characters’ Rumspringa, or “running around” years, the time when the Amish lift the stringent rules for courting youth.

Lewis’ books in particular are an antidote to overstimulated nerves. The Amish (who number about 230,000, mostly in Pennsylvania, Ohio and Indiana) are notable for what they reject — from televisions to electric kitchen appliances to zippers — which means a quiet environment for readers. The pace is slow and soothing; no conversations in Bird-in-Hand are interrupted by a ringing cell phone.

Still, simplicity doesn’t necessarily mean serenity. In The Secret, Lettie Byler, a troubled wife and mother in a devout Amish home, is, for some mysterious reason, depressed and tearful. Eventually she disappears into the night, in what is “surely the most remarkable tittle-tattle to hit the area in recent years.” Englischers (i.e., the non-Amish) might have steered Lettie into a psychiatrist’s office for a course of Prozac. But Lettie’s large family has other modes of counsel: talking and cooking and harvesting and raising barns and praying together. Her 21-year-old daughter Grace holds the family together with her steely determination; Judah, Lettie’s uncommunicative husband, suffers her absence deeply.

It hardly sounds like the stuff of controversy, but Lewis’ novels have been banned by some Amish leaders in Ohio because of theological differences. Perhaps unsurprisingly, that has not prevented the books from reaching an Amish readership. Lewis has received thousands of letters over the years from Amish fans. “I don’t want to mislead you, Mrs. Lewis,” confided a correspondent. “All of us are reading them under the covers.” Barnes & Noble’s religion-book buyer, Jane Love, confirms that sales are particularly strong in Amish areas. (See the 100 best novels of all time.)

Lewis came to the subject as a matter of genealogy. Her grandmother was a horse-and-buggy Mennonite who was shunned by her community for marrying a covenant preacher. “It was a very courageous move for her,” says Lewis. “She was 18 when she left. She took off her head covering, and she decided that she was going to wear a simple gold wedding band, and she was excommunicated.” Lewis’ first novel, The Shunning, which told that story, was a surprise hit that sold more than a million copies. In all, she has written 87 books, many for children and teens.

Like her fellow chroniclers of the Amish, Lewis proves that it isn’t necessary to lace every scene with lust to keep the reader’s attention. Grace’s suitor in The Secret tenderly proposes to her without ever having kissed her. “‘Tis mighty gut,” he says with deep affection. “Will you agree to be my bride?” That scene is not likely to be repeated outside Lancaster County anytime soon, but Bird-in-Hand is an appealing place for a jaded Englischer to escape to for a while — which is part of the romance, after all.