Japanese Ramen, though infused with culinary heritage, is hardly a traditional dish. It’s actually a fairly modern invention, a mash-up of Chinese-Japanese cuisine popularized after World War II when cheap flour from the U.S. swept the Japanese market. Still, ramen lovers are a captious crowd and the noodle soup has spawned something of a cult following, particularly in the South Bay.

So when Kha Lu began experimenting with the flavor profiles of ramen at his new lunchtime pop-up eatery, Kansui, customers got a bit defensive.

“People freaked out,” says the chef, an alumnus of Plumed Horse in Saratoga and Charlie Trotter’s Michelin-starred Chicago establishments. “We can get pretty whimsical with the ramen.”

Since launching Kansui with Hay Market chef-owner Joe Cirone in January, the ramen offerings ($10-$12, bowl) have featured a global amalgam of flavors, all with house-pulled noodles and a whole seasoned egg. Five-spice duck ramen. BLT ramen with braised bacon and spiked tomato broth. Red curry ramen. Reuben ramen with goat pastrami and pumpernickel noodles. Duroc pork belly ramen. Ramen de pollo with masa noodles, coriander, lime and crema Oaxequeña. Chinese herb ramen with ginseng, dates, longan and dandelion greens. And vegetarian—a rarity in the local ramen scene.

Earlier this month, Lu introduced duck confit ramen, served with a crispy duck leg and a heap of noodles doused in an oily sherry-citrus broth topped with seaweed, bamboo shoots and green onions. Breaking up the richness, an unusual addition: pickled shiitake mushrooms.

Lu adds them to several of his ramens, even the more common variations like miso, shio, shoyu and the 72-hour pork-bone tonkotsu.

“We’ll keep the staples,” says Lu. “We’ll stay with a small menu and focus on making it really, really good.”

Kansui opens from 11:30am to 1:30pm, Tuesday through Saturday, out of Cirone’s farm-to-table Hay Market in Willow Glen. It’s a completely different restaurant during the day, which initially confused folks.

“It was sort of a punch in the face for Willow Glen,” says Cirone, the guy who hosted Anthony Bourdain’s after-show shindig last year. “People came in asking what happened to the burgers, the hot dogs, the food they were used to.”

Lu and Cirone caved and put a burger on the menu, but, of course, with a Japanese twist. The okonomiyaki burger ($11) comes served between half-sourdough, half-okonomiyaki buns and wok-fried cabbage with smoky bonito fish flakes that curl as they wilt from the heat.

The plan is to keep the menu tight, to focus on the main course. Lu also offers small plates of savory seared cabbage-topped okonomiyaki cakes ($7), edamame ($5), hot wings ($10), pickled sockeye salmon ($9) and beef tripe chili ($7). To drink, there’s a range of chilled or warm sake and beers by the bottle or on tap.