By 9:15 a.m., the broths are all simmering, chicken, beef and vegetarian just barely at a bubble. Chau Du is preparing for what she expects will be an average lunch at Pho Co. in Portland, a prediction based mostly on the weather. It’s not raining, it’s not particularly cold and so she is making merely enormous, rather than gigantic, vats of broth in a trio of approximately 30-quart stockpots. They already smell good, with notes of cinnamon and star anise rising up. In the beef broth, a couple big chunks of ginger root bob at the surface, floating alongside five long bones.

Every day except Sunday, Chau Du makes broth for her food stand, which she opened in December with the help of her husband and business partner, Hoang Nguyen. On the rare day that she has leftover broth – Pho Co. has been a popular addition to the Public Market House in Monument Square – she still starts over the next day, looking for the kind of purity of flavor that she believes results from a batch made fresh that morning.

A giant bucket of rice noodles sits nearby and her assistant, Ngoc Ha, is tearing basil leaves off stems. They go through a five-pound bag every couple of days. The space is tiny, but this is a serious pho factory, headed by a woman who is her own toughest critic.

Six months ago, Du was a rag cutter at Goodwill Industries of Northern New England – making what Goodwill branded as Good Wipes, cast-off items like old T-shirts that cutters turn into neat squares of cloth for industrial uses: scrubbing, soaking up spills and so forth. Hers is an immigrant story, but not the one many might expect.

Chau Du did not come to America with secret family recipes and a lifelong dream of opening up a restaurant. A decade ago she didn’t even know how to cook. But when she fell in love with an American and prepared to move to Portland to be with him, she gave herself a crash course in Vietnamese cooking. Via YouTube, with an assist from her mother.

Customers wait for their orders at Pho Co. Pho is everywhere in Vietnam, but Chau Du didn’t learn how to make it until she emigrated to the U.S.

THE UNIVERSITY OF YOUTUBE

If you pick up pho at Pho Co., you might not even notice Chau Du, quietly working away in the back, skimming froth off the broth or shredding chicken for the pho. Nguyen translates for her during a first interview, although her English is strong enough to have seen her through waitressing jobs at Saigon and Veranda Thai in the eight years since she arrived in the United States. His theory is she’s still shy about speaking English in front of him, even though his Vietnamese was terrible when they met (“It was like second- or third-grade Vietnamese,” he says). Her take: He explains it better.

In Saigon, where Chau Du grew up, pho was omnipresent. It might come from a street cart for lunch or be delivered in the morning for breakfast, but she never had to learn how to make it. She worked in the family business, a clothing store along the lines of Forever 21, and only started to thinking about cooking as a skill she wanted to acquire after she met Nguyen in 2007. He was on a rare visit to the country of his birth, attending the wedding of a cousin, when a friend introduced them.

“I asked her out on a couple of dates,” Nguyen said. “And that was that.”

Nguyen had moved to Portland when he was 8 years old, part of a refugee resettlement program for Vietnamese families with children fathered by American servicemen, as his older sibling was. Catholic Charities of Maine helped his mother resettle in Portland after the family had spent a year in the Philippines learning English and preparing for the transition. Nguyen went into the restaurant business himself as a college student at the University of Southern Maine – running the now-closed Bottomz Up on Munjoy Hill – but ultimately quit to focus on his studies. He majored in economics and started working as a financial writer for The Corporate Library, a research and risk rating firm now owned by MSCI.

It took two years from their meeting for Chau Du to join Nguyen in Portland. They had married and she had given birth to their son before the immigration paperwork allowing her to move to the United States came through. During that time, she studied YouTube videos, with what her husband would learn was a fierce determination to learn.

Du’s beef broth, with big chunks of ginger root simmering amid beef bones.

At first, Nguyen said, she was afraid of using the butcher knife – the first dish she made him was braised pork with eggs, and her nervousness showed. The first time they had home-cooked pho, he made it. “Now of course she is millions of miles ahead of me,” he says.

By the time Chau Du started working at Goodwill in 2011, she’d achieved the skill level that made her supervisor there, Mike Howe, gravitate immediately to the dishes she’d contribute to the company potlucks.

“She made a mango salad that was very good,” Howe said. There were spring and egg rolls. Of particular note were her tofu triangles with peanut sauce, he said. At home, Du practiced dishes on family, with Nguyen serving as chief tester and critic. She kept trying to work out the kinks in a Bun Rieu Cua Crab noodle soup. She is, he said, “like an artist always working on a new masterpiece.” They started to talk about opening a restaurant someday. His sister-in-law owns Huong’s Vietnamese on St. John Street, so the idea was very much in keeping with the family business. But they had a second child, a daughter now 2, and getting into a business that would require long hours in the evening wasn’t appealing.

HOME FOR DINNER

Then Nguyen saw a Craigslist ad for the spot on the second floor of the Public Market. Du could close the stand by 6 p.m. and be home for super. Working downtown himself, and often rushing through lunch, he had in mind the concept of a pho stand that served more portable portions, sized for 30 minutes at a desk instead of a full lunch hour. He floated the idea with her. She was nervous. “She’s humble,” he said. “She had no idea if people were going to like it or not.”

He built the booth for the stand, which is so small that there is barely room for her assistant and a counter person. He asked a friend to paint a sign for them and then gave Du a little push. They opened in December. With each customer who stops by to comment on how good or how rich the broth is, her confidence has grown, although still, the perfectionist in her anxiously tends that broth.

Those kind of high standards should serve her well. Vietnamese food expert and cookbook writer Andrea Nguyen, whose latest book is “The Pho Cookbook,” said in an email that “excellent pho depends on quality ingredients, skill, and thoughtfulness. A good pho shop makes its broth on a daily basis.”

Chau Du fills an order at Pho Co.

Does Du miss the land where this soup originated?

“I miss the weather,” Du said. “And my family and my friends.”

In February, for the first time since she joined Nguyen in Maine, she traveled back to Vietnam for a month, arriving in time for the Asian New Year celebration. The tickets had been bought last year, before Nguyen’s Pho Co. brainstorm. It can’t have been easy to break momentum with a new business, but Du’s grandparents are in their 90s, and they were desperate to see her. If she didn’t come soon, they told her, they would die.

She pressed her fingers to her eyes to stop tears, then waved off sympathy over homesickness, Maine winters, ancient loved ones.

“You have to keep going,” Du said. “Because life is not easy.”

On that visit, all her relatives, her aunts and uncles and cousins, wanted to do was feed her and Nguyen, to take them out to eat. Her grandparents had seen glimpses of Pho Co. via her cousin’s Facebook account. But still, they didn’t quite believe it.

She cooked for them. Pho and Bun Rieu. They were convinced. She had their blessing to go back to her life in Portland.