Vietnamese Spicy Beef Noodle Soup

Beef shank simmers for hours at low heat to yield a rich, collagen-heavy stock, and it is into this base that dried chilies, lemongrass stalks, and a measured quantity of mam ruoc, the fermented shrimp paste specific to central Vietnam, are introduced, building a spiciness that is complex rather than simply hot. A bright-red slick of chili oil floating on the surface signals the heat level before the first sip, and that first spoonful delivers the deep umami of the shrimp paste layered beneath the citrusy, grassy brightness of lemongrass, a combination unlike anything in other Vietnamese noodle soups. The noodles, called bun, are thick, round rice noodles chewier and more substantial than the flat strands in pho, with enough body to stand up to the heavy, assertive broth without becoming waterlogged. Bean sprouts, shredded raw banana flower, and a squeeze of lime are served alongside and added at the table, where their crisp textures and sharp acidity cut directly through the richness and temper the heat. Sliced pork blood sausage and braised pig's knuckle are the traditional additions that bring the bowl into full alignment with what is served in the street stalls of Hue itself.