The dish wasn't invented in Bicol at all — it was named and popularized at a restaurant in Malate, Manila, after the sound of a passing train reminded its creator of the rail line running to the Bicol region.
Pork is simmered low in thick coconut milk with shrimp paste, garlic, and a heavy dose of long green and red chilies until the sauce reduces into a rich, fiery coating. It's ladled hot over rice at carinderias and food stalls across the country, though it hits hardest at stalls in its namesake region.