Heat the vegetable oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Add the beef cubes in a single layer and sear until deeply browned on all sides, about 6-8 minutes.

Add the chopped onion, minced garlic, and grated ginger to the pot. Sauté for 3-4 minutes until the onions are softened and fragrant.

Stir in the bruised lemongrass stalks, star anise, five-spice powder, fish sauce, and soy sauce. Cook for 1 minute until the spices are highly aromatic.

Pour in the beef broth, scraping the bottom of the pot with a wooden spoon to release any browned bits. Bring the mixture to a gentle boil.

Reduce the heat to low, cover the pot, and let it simmer gently for 1.5 hours, or until the beef is mostly tender.

Add the sliced carrots to the stew. Cover and continue to simmer for another 30 minutes until both the beef and carrots are completely fork-tender.

While the carrots are finishing, prepare the rice noodles according to the package directions. Drain well and divide the cooked noodles among four serving bowls.

Remove and discard the lemongrass stalks and star anise pods from the stew. Ladle the hot beef stew over the noodles, garnish with fresh cilantro, and serve with a wedge of lime.