The Berkowitz family of Ambler gathered Tuesday for their traditional Christmas dinner: wonton soup, pan-seared pork dumplings, salt-baked shrimp and scallops, orange beef and sweet-and-sour chicken.

"So it is written, so it shall be done," attorney Michael Berkowitz said between bites at Lee How Fook in Chinatown.

He was only half-joking. As sure as Jews pack synagogues on Yom Kippur, the Day of Atonement, so do they eat in Chinatown on Christmas.

"You want to know why?" teased Berkowitz' mother Phyllis, who drove in from Allentown with her husband Newton.

"Trad-i-tion...tradition!" she sang, mocking Tevya the Milkman from Fiddler on the Roof.

For many Jewish families, eating in Chinatown on Christmas is almost an 11th Commandment. So practiced is this custom that Lee How Fook had to stop taking reservations several days ago and posted a CLOSED sign on the door to discourage passersby.

"This is our way of celebrating the day off," said Beth Berkowitz, Michael's wife and the mother of their children Josh, 8 and Rachel, 13.

Christmas is, after all, a national holiday.

Schools and offices are closed for Jews and Muslims, too. Many volunteer at hospitals and homeless shelters, or work extra hours at their day jobs, filling in for Christian colleagues.

But there's still time to eat. Chinatown offers casual prices and a nonsectarian atmosphere devoid of sparkling trees and waitstaff in red stocking caps.

"Most of us are Buddhists," said Peter Fong, the chef-owner of Singapore Kosher Vegetarian Restaurant on Race Street. "We don't celebrate Christmas, either."

Fong, who came to the United States from Malaysia 16 years ago, first imagined Singapore as a strictly vegetarian restaurant. But quickly customers suggested that he seek the rabbinic certification required of kosher restaurants.

Judaism has different denominations, he learned, and some are more strict than others. The less traditional do not observe the strict dietary rules that forbid, for example, eating pork and shellfish, or serving meat and dairy at the same table.

That's why the Berkowitz family had real pork at Lee How Fook, while at Singapore: the "pork" is actually all-vegan seiten.

Over the years, Fong learned that his beloved potato pancakes - a dish he thought was unique to the North of China - were also known as latkes. And now he casually refers to the wontons in his soup as kreplach and to his steamed dumplings as kneidelach.

He re-applies annually for certification from the Rabbinical Assembly Mid-Atlantic Region, and donates dinner for elderly members of Congregation Beth El in Yardley "because they are used to eating Chinese, too, on the holiday but they can't come into town anymore."

Like so many of the Chinatown restaurants, Singapore is bigger than it looks.

Table for 53? No problem. That's how many parents and children were at Singapore today for the Perelman Jewish Day School's annual outing. They picked a multi-course menu that featured General Tso's Chicken, Vegetable Lo Mein and Sweet and Sour Pork - all made with tofu or seiten in lieu of meat or poultry.

The school, with locations in Merion and Melrose Park, encourged families to bring socks, shampoo, and scarves for delivery after lunch to St. John's Hospice on Race Street.

Lisa Richman, a Perelman teacher who organized the lunch, said so many families go to the movies afterward that she made up a list of theaters showing G and PG rated films and their show times.

That balances nice with the unofficial list distributed annually at the National Museum of American Jewish History.

"Every year, we have a program for Jewish families with young children," said museum spokesman Jay Nachman. "And every year, families ask which of the restaurants in Chinatown are kosher. So I began handing out a little list."

Contact staff writer Dianna Marder at 215-854-4211 or dmarder@phillynews.com. Read her recent work at http://go.philly.com/diannamarder