01 - Season beef cubes generously with kosher salt and black 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 cubes until deeply browned on all sides, approximately 3-4 minutes per batch. Remove browned beef and set aside on a plate.
03 - In the same pot, add onion, lemongrass, garlic, ginger, and red chilies if using. Sauté for 3-4 minutes until fragrant and onions have softened, stirring occasionally to prevent burning.
04 - Stir in fish sauce and brown sugar, cooking for 1 minute to allow the sugar to dissolve and flavors to meld.
05 - Return the seared beef to the pot along with any accumulated juices. Add coconut milk, beef broth, and carrots. Bring the mixture to a gentle simmer, stirring to combine.
06 - Reduce heat to low, cover tightly, and braise for 1 hour. Maintain a gentle simmer throughout.
07 - Add quartered mushrooms to the pot, stir gently, and continue braising covered for an additional 1 to 1.5 hours. The beef is ready when it yields easily to a fork.
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 over steamed jasmine rice or rice noodles, generously garnished with chopped fresh cilantro, sliced scallions, and additional lime wedges on the side.