It begins innocently enough: You have your first taste of pho somewhere like Golden Deli, the noodle shop on the outer reaches of San Gabriel, where the fragrant, stunningly clear broth is as famous as the crunchy egg rolls. Like any proper gateway drug, you soon begin to run the gamut of chintzy pho parlors up and down Valley Boulevard, which in turn reveals the less common, more intense style of cooking from central Vietnam — the harder stuff — spicy, sour bowls of bun bo hue, and the smoky, banana-leaf bound meatballs called nem nuong.

Somewhere down the road you end up at Ha Tien Quan, a former Cantonese noodle shop converted so recently, its owners haven't had time to swap out the posters of Hong Kong nightlife lining the walls. The specialty — or dac biet — here is a dish called bun mam, a hyper-regional creation known colloquially as “Vietnamese gumbo,” most popular in the country's southwestern tip, where the Mekong River fans out into countless little fingers and forms an ultra-fertile swampland equal to the size of Switzerland.

Compared with the relative tameness of pho, Ha Tien Quan's bun mam is a tab of high-proof blotter acid — a booming, murky kaleidoscope of sweet umami funk. Imagine a rich heady stew, flavored with lemongrass, ginger and garlic — stocked with thin rice noodles, plump prawns, strips of braised pork belly, chunks of tender catfish and long strands of flat-leaved chives. The proprietor drops off a plate of a half-dozen or so aromatic herbs and a wedge of lime, for garnish.

The key to proper bun mam, he tells you, is mam ca loc, a potent paste of fermented anchovies that comprises most of the soup's base. It's as thick as toothpaste and odiferous enough to make a wheel of old Roquefort smell like an air freshener. Owner Larry Ta, a former machinist turned restaurateur, imports his own mam from a relative in Vietnam, and swears his soup has no equal in all of California. I, for one, am inclined to believe him.

The family that runs the kitchen originally hails from Ha Tien, a small border town at the headwaters of the Mekong Delta, best known for being the jumping-off point for secret Cambodia incursions made by the CIA during the Vietnam War. A good deal of the menu is dedicated to South Vietnamese favorites: com tam, broken nubs of steamed rice paired with things like coconut milk-glazed pork chops; and hu tieu, a wide egg noodle cribbed from Chinese cuisine. A less advertised special is hu tieu soup, brimming with slices of deer meat and an oily paste made from crushed chiles. There's also something called bun nuoc ken, a strangely compelling bowl of vermicelli heaped with a mixture of minced catfish, curry powder and coconut milk, sort of like an Asian riff on tuna noodle casserole.

You probably also should try the cha gio re, a variant of the crispy egg roll where a latticework of rice noodles is subbed in for the usual wrapper, or banh knot, miniature, saucer-shaped egg crepes filled with ground shrimp and bits of pork. You bundle them in large swaths of lettuce and dip them in sweet fish sauce and take a big bite — a rhapsody of crisp and crunch.

For dessert, there is special Ha Tien gelatin, a multicolored layering of coffee, pandan and coconut flavors. Or you could simply sip on a cup of extra-strength iced coffee, thickened with enough condensed milk that it practically amounts to a milkshake.

Vegetarians, take note: Every quarter-moon and three-quarter moon, Ha Tien Quan serves only meat-free versions of its dishes, in accordance with Buddhist traditions (if you've ever sampled vegetarian Vietnamese food, you'll know this is a tantalizing treat rather than a drawback). Check your nearest lunar calendar for details.

Ha Tien Quan: 529 E Valley Blvd., Ste 178A, San Gabriel, (626) 288-1896

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