Kansui is full of surprises.

Here are two to know first: This lunchtime ramen shop in San Jose's Willow Glen neighborhood is open only 10 hours a week. And it's housed -- with no signage -- inside an entirely different restaurant.

A hidden gem, indeed.

Kansui, which is sometimes referred to as a "pop-up" restaurant, serves steaming bowls of ramen and other specialties inside the decidedly un-Japanese Hay Market eatery. So if you're standing in front of Hay Market's oversized turquoise door and hay bales, you're in the right place.

House-made noodles and rich, complex broths make the standard ramen incredibly satisfying.

The buttery broth in Tonkotsu ($10) is steeped with meaty flavor pulled from a 72-hour soak of pork bones. The savoriness is intensified by two planks of chashu -- or pork belly -- braised in shoyu, garlic, ginger, mirin, reduced sake and brown sugar. The zing from pickled shiitake mushrooms and fermented bamboo nicely balances the smooth and slurpy broth, and a soft-boiled egg bobbed along in the bowl. The soup is prettily finished with a large square of nori that rises from the dish like a sail.

But why just have ramen when there are "dipping noodles" to be had? Kansui Tsukemen ($13) is a fun deconstruction of the regular soup, also beautifully presented in a trio of bowls on a long wooden board.


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A bowl of brown-flecked toasted rye noodles sits at one end of the board. The noodles are served cold, but two kinds of hot broth will take care of that. In one bowl is soy-garlic tare, a thick and briny sauce flavored with roasted chicken, shoyu and garlic. It is reduced three times over, to resemble a dark brown gravy. Next to it is a bowl of a light ramen broth; use it to thin out the tare until it suits your personal taste.

At the other end is a fun heap of treats, including bamboo, pickled mushrooms, a halved soft-boiled egg and soft, subtly sweet seaweed. There was also thinly sliced pork belly that was far meatier and less fatty than I expected. I enjoyed mixing up the bites in my bowl. And do try a sprinkle of the seven-spice chili that sits in tiny glass dishes on the table. It's not quite as hot as it looks and contains a tinge of citrus.

Here's another surprise: The best thing on the menu might not even be ramen. Okonomiyaki is a savory Japanese pancake, and our server wisely steered us toward the Dry Creek Bacon Okonomiyaki ($9), which had me and my companion swooning. The quichelike patty -- eggy on the inside, crisp on the outside -- is served in a small cast-iron skillet. The pancake is studded with cubes of bacon as well as scallions and wok-fired cabbage, then topped with delightful bonito flakes. These featherlike pale pink shavings of dried fish not only added a burst of umami but also a touch of drama -- they are so thin that heat causes them to wave lifelike, to and fro, across the top of the pancake.

And if you like the okonomiyaki as much as I did, try having it ... in a burger! This $12 sandwich is not to be missed. A juicy beef patty is topped with the best parts of okonomiyaki -- including a luscious sweet-mayonnaise sauce fused with bonito -- and served inside a golden-brown square bun that was airy and moist but sturdy enough to hold all that flavor.

The menu changes with some frequency, as Kansui chef Kha Lu likes to experiment. Tonkotsu was such a popular special that it landed a permanent spot on the menu. Other past specials have included squid-ink noodles in crab broth and pumpernickel noodles with goat pastrami.

Sounds like good reasons to return again and again.

Contact Amy Pizarro via food@mercurynews.com.

KANSUI

1185 Lincoln Ave., San Jose
408-295-4800; www.kansuiramen.com

Hours: 11:30 a.m.-1:30 p.m. Tuesday-Saturday
Types of food: Ramen, of course -- plus okonomiyaki, edamame and burgers
Average price: $10
Good choices: Dry Creek Bacon Okonomiyaki ($9), Tonkotsu Ramen ($10)
Not recommended: The salt on the edamame ($4) got to me after a few bites.
Vegetarian options: There are a few, including a vegetarian ramen.
Drinks: Sake bomb! Plus a full bar that includes beer selections and all of Hay Market's craft spirits and cocktails; also tea, lemonade, soda, ginger beer and root beer
Attitude: Friendly and attentive. Restaurant owner Joe Cirone frequently makes the rounds to check in with diners and answer questions about the food.
Credit cards: Accepted
Parking: On the street or in nearby lots

Restaurant reviews are conducted anonymously. The Mercury News pays for all meals.