01 - Season beef cubes generously with salt and pepper, ensuring even coverage on all sides.
02 - Heat vegetable oil in a large Dutch oven over medium-high heat. Working in batches to avoid overcrowding, sear the beef until deeply browned on all sides. Remove browned beef and set aside.
03 - In the same pot, add onion, lemongrass, garlic, ginger, and chilies if using. Sauté for 3–4 minutes until fragrant and onions have softened.
04 - Stir in fish sauce and brown sugar. Cook for 1 minute to allow the sugar to dissolve and flavors to meld.
05 - Return the seared beef to the pot. Pour in coconut milk, beef broth, and add carrots. Bring the mixture to a gentle simmer.
06 - Reduce heat to low, cover tightly, and braise for 1 hour to begin tenderizing the beef.
07 - Add quartered mushrooms to the pot, stir to incorporate, and continue braising covered for another 1 to 1.5 hours until beef is fork-tender.
08 - Remove and discard the lemongrass stalks. Stir in lime zest and juice. Taste and adjust seasoning with additional salt if needed.
09 - Serve hot, generously garnished with chopped cilantro, sliced scallions, and fresh lime wedges on the side.