We met in Chinatown.

She could tell it was me because I was holding a sprig of mugwort, waving it gently. People were looking at me side-eyed, then walking quickly by.

We didn't waste time or words. We were on a Mission Almost Impossible: Find mugwort flour, aka in sai or lin sai flour, a dried and ground herb used in making in sai biang, molded steamed cakes served in celebration of certain Chinese festivals.

Reader Robin Fong had written in June to ask how to make in sai biang. After several readers responded with recipes (thank you, Millie Chang, Carol Wong and Jeonora Chang), I thought my work was done.

Ha! Turned out all the recipes called for in sai flour or ground fresh in sai leaf.

My only clue was Fong's vague memory — which turned out to be accurate — that in sai is what English speakers call mugwort.

But what is mugwort?

The Internet had that answer: Mugwort is a hardy weed; in Latin, Artemisia, a member of the Asteraceae family and a relative of the aster, the chrysanthemum and our own endemic 'ahinahina, as you can see in its notched leaves with silvery backs. The variety most often used in cooking is Artemisia vulgaris, but other types are also used. All the major Asian cultures prize mugwort for its fragrance and its medicinal properties, using it in teas and for various treatments.

Chinese call mugwort ai yeh and use it not only to make rice flour cakes but to attract good luck at New Year's (tie small bunches to the door on the first day of Chinese New Year). Hakka Chinese make sticky pork buns with mugwort flour for Ching Ming, Tomb Sweeping Day, April 5. Japanese call mugwort yomogi and employ it to make a special light-green mochi, kusamochi, for Dolls' Day, and also a type of soba noodle. Koreans call it ssuk and use it in hand-formed rice cakes to celebrate Suri Day, a spring festival.

All good to know. But where, oh where, do you get mugwort or mugwort flour in 21st-century Honolulu?

Enter Marylene Chun, who saw a mission and chose to accept it.

A longtime e-mail acquaintance who is passionate about cooking and baking, Chun remembered making in sai biang with her popo Chun Lai Shee. She had cousins lined up for days for the recipe (her grandfather, C.Q. Yee Hop, had 17 children). Ask any Chinese over 40 and they'll remember in sai biang, but you need to go to the over-60s to find anyone with a clue how to make the cakes.

Popo Chun Lai Shee used to make literally hundreds of the hand-crafted cakes at a time, but little Marylene was never involved in assembling the dough. Her job was to press knobs of dough into the well-oiled wooden forms (rather like German springerle molds), then remove and trim them so Popo could steam them.

Once a year — Marylene doesn't remember when — each child's family got a packet of the flat, embossed, green cakes. One cookbook says the cakes are associated with a festival celebrated on the eighth day of the fourth lunar month (spring or early summer). We were unable to find out which festival that is, but spring or early summer makes sense, because mugwort is said to be at its tender best at that time of year (at least in cold Japan and Korea, where it doesn't grow year-round).

But back to the Chinatown mission.

Marylene had already scored a triumph by persuading Marukai produce manager Dennis Yamachika to get his secret source — said to be a local lettuce farmer, but he wasn't telling — to cut a bunch of fresh mugwort for us. I had gone down to Marukai to pick it up; he had to hide the leaves in the back, he said, because if he put them on display they'd be gone in a Tokyo minute. Usually, Marukai only brings fresh yomogi in at New Year's, when local Japanese like to make the green mochi cakes. The store does, however, sometimes carry yomogiko (powdered mugwort); I found it near the mochi flour, in 1.5-ounce cellophane packets.

We never did find another source of fresh yomogi — neither Shirokiya nor Daiei deals in it. But Marylene — who missed her calling as a detective — found out you can order plants from Home Depot.

Packing my groceries at Marukai, I had to defend the mugwort against the covetous designs of a Korean woman who stopped dead when she saw the leaf and demanded, "Where you get that?"

I explained it was a special order.

"Medicine, you know! Good for liver, good for womans, good for all kinds." She reached right into my cart and grabbed the bunch, taking a deep sniff of the leaves.

I figured I'd impress her with my one word of Korean.

"You call this ssuk?"

"Yes! You know," she answered, breaking into a smile. There followed a spirited conversation, partly through gestures, in which we agreed that, yes, it was good for you, yes, it made good rice cakes, yes, it was hard to find, and yes, that was too bad. Both of us stood meditatively munching the leaves, which taste like chamomile to me and smell like black tea.

Somehow, I got out of Marukai with my mugwort intact.

A lucky thing. It was a leaf from the Marukai bunch that was our talisman as we scoured Chinatown a couple of days later. (Fresh mugwort, by the way, lasts beautifully for a week if you trim the stems, place the bunch in a pitcher of water and store it in the refrigerator.)

I waved that mugwort all over Chinatown while herb sellers and grocers shook their heads and sent us away.

Neither of us speaks Chinese, and our attempts to pronounce "ai yeh" and "in sai biang" without knowing how to give them the right tones met with blank looks.

At Fook Sau Tong herbalist, chrysanthemum, yes; ai yeh, no.

At Hing Mau grocery, never heard of it.

At Bo Wah store, Marylene used sign language to describe in sai biang and he waved her toward a shelf where he had a number of different models. I bought a couple at $2.75 apiece, but we couldn't find in sai flour anywhere. While I was paying for these, the grocer gestured to the mugwort in my hand. "What is that?" he asked. Marylene turned to me and said, "If I wasn't with you, this is the point at which I'd give up."

At New Chee Wo Tong herbalist, a gathering of gossiping men fell silent as we walked in. The one who seemed to be in charge shook his head and waved us away as we explained what we were looking for. Marylene persisted. They all gestured to a man in a white undershirt who spoke English. Light dawned when I showed him the molds and Marylene went into her sign language act. "Ah, in sai biang, in sai biang," he says, pronouncing it with the proper intonation so that everyone in the place began nodding. And then shaking their heads. Because, no, they don't have any in sai flour.

Our translator engaged in a spirited explanation of how the cakes are made that confirmed Marylene's memory that you have to use rice flour, not sweet rice flour (mochiko). "Maybe sometime somebody grow in their yard," he suggested helpfully. (And, indeed, we heard from several sources that yomogi is primarily a garden plant here.)

All through Maunakea Marketplace, the heads kept shaking. The only joy we got was at Ace Market on King Street 'ewa of Oahu Market, where a fruit and vegetable seller that Marylene knows said he does sell fresh mugwort — but only around New Year's.

A couple of days later, Marylene and I reconvened in my Kamehameha Heights kitchen for a marathon in sai/yomogi testing session, using a combination of fresh and dried mugwort to make mochi cakes and in sai biang.

It took her four tries to get the rice flour-to-water proportion right for the in sai biang, so that the cake's texture was properly smooth and springy-tender and the cakes cooked through. She actually got chicken-skin when she smelled the boiled fresh mugwort for the first time. "That's when I knew I was on the right track," she said.

The cakes are a monumental amount of work — the thought of Popo making a couple of hundred at a time leaves us in awe. And the taste, a sharpish vegetal flavor of chamomile, black tea and cooked spinach, might be too medicinal for some. But the final batch of cakes was lovely to look at and we gazed on them like proud parents on a newborn.

My much easier microwave yomogi mochi cakes tasted fine but — I gotta say it — they looked as though they'd been made by a haole. Gotta get somebody to show me how to shape them properly.

But that's another Mission.