One in a series on iconic New England eateries.

WOONSOCKET, R.I. — Back in the 1950s, George Laferti hit on a winning formula for a quick, satisfying meal. From his “Rolling Castle,’’ a cart that he towed behind his car, he sold French fries with vinegar and his own recipe for “dynamite’’ sandwiches, a Woonsocket variation on a sloppy joe.

Eventually the cart became a restaurant so small that diners and cooks were crammed into the same tight space. Looking for a summer job after she graduated from high school, Diane Frenette began working at the Castle and ended up staying until she left to start a family. When the Castle came on the market in 1986, she and her father purchased it, and the family eventually added a comfortable dining room on the back.

“I’ve been with the Castle for 37 years,’’ says Diane, who shares duties with her daughter Jesse Frenette, who started helping out when she was in middle school.

The Castle is a mainstay of Woonsocket life, a place where people enjoy a side of gossip with their meal. Ask any of the road crew workers, police, delivery van drivers, or patrons of the adjacent Elks Club — there’s a yawning gap in the daily patter when the restaurant closes for the season in December. The first meal in the spring, usually in early March, is almost like opening day at Fenway Park — or McCoy Stadium in nearby Pawtucket.

Over the years Diane has expanded the menu. “We’re from a big family — we cook,’’ she shrugs. Every day she offers several homemade soups, salads, sandwiches, and dinner plates such as sirloin steak tips or liver and onions. Daily specials might include fish and chips or “French meat pie’’ for Woonsocket’s large French Canadian population.

But as in Laferti’s day, dynamites and fries are the backbone of the menu. “I sell tons of dynamites,’’ says Diane. “I make two big batches a week.’’ She estimates that she sells about 200 pounds of dynamites a week. “It doesn’t end,’’ she says.

A Rhode Island food specialty so limited that it’s hardly known outside Woonsocket, the “dynamite’’ is like a grown-up version of the school cafeteria sloppy joe — except that it’s more flavorful, less salty, and has a bit of a lip-warming, tongue-tingling punch. Diane doesn’t divulge her recipe, but it’s clear that her version has lots and lots of coarsely chopped green pepper and celery and a touch of hot pepper in the tomato-based sauce. It is about three parts meat and vegetables to one part sauce.

That proportion makes it possible to ladle the mixture onto a soft grinder-style roll, the traditional way to serve a dynamite. Some Woonsocketers prefer the dynamite sauce spooned over a hot dog (the dynadog), over a hamburger (the dynaburger), or over a plate of pasta like a Bolognese sauce with serious Rhode Island attitude.

No one should visit the Castle alone, because two people can order their dynamites of choice and split side orders of French fries and onion rings, which are always fresh, never frozen. The onion rings are peeled and cut by hand, double dipped in breading mix, then quickly fried at a high temperature until they are sweet and the thin coating is nutty and crisp.

Diane and Jesse are equally fussy about the French fries. “We go through a quarter ton of potatoes a week,’’ says Diane, who points to a barrel-like mechanism in one corner of the kitchen. “That’s an industrial potato peeler like they use in the Army,’’ she explains. All those russets may be peeled by machine, but they are hand-cut to long batons that cook up golden brown.

True to tradition, the tables have vinegar shakers next to the ketchup. George Laferti would have approved.

CASTLE RESTAURANT 420 Social St., Woonsocket, R.I. 401-762-5424. Open 11 a.m.-7 p.m. Mon.-Sat. Sandwiches and plates $2-$21.95 (most plates $8.25-$10.95).

Contact Patricia Harris and David Lyon can be reached at harrislyon@gmail.com.