Budu is where the South begins. Cross south of Chumphon and the nam pla (fish sauce) bottles start disappearing from tables. In their place: thick, dark, fermented anchovy sauce with a funk that hits you from across the room. That's budu. And nam budu, the cooked dipping sauce made from it, is the condiment that ties the entire Southern Thai table together.

Ajarn always said the four pillars govern all Thai cooking: fish sauce for salt, palm sugar for sweet, tropical fruit for sour, chili for heat. Nam budu follows every one of those rules, but it swaps the salt pillar. Down south, budu replaces standard nam pla in dozens of preparations. It's thicker, darker, more intensely fermented. The umami is deeper. The aroma is, let's say, assertive. If nam pla is a handshake, budu is a bear hug that won't let go.

Making nam budu is simple. You cook the raw budu with palm sugar, shallots, and chili until it thickens and the sugar dissolves. Then lime juice goes in off the heat, because Ajarn's rule holds: add sour last, add sour slowly. The result is a thick, sweet-salty-sour-spicy sauce you spoon over rice, dip vegetables into, or drizzle across fried fish. It's the ketchup of the deep south, except it actually tastes like something.

I learned to appreciate budu late. Growing up in Bangkok, I knew nam pla. Budu was something I smelled at a Songkhla market during a trip with Ajarn and nearly walked away from. He grabbed my arm. "Smell that again. That's protein breaking down into amino acids. That's fermentation doing the work of a thousand hours. Respect it." I stood there and smelled it again. He was right. Once you understand what budu is, the funk becomes the point.