01 - Rub beef cubes thoroughly with kosher salt and black pepper, ensuring even coating on all sides.
02 - Heat vegetable oil in a large Dutch oven over medium-high heat. Sear beef in batches until browned on all sides, about 3-4 minutes per batch. Transfer browned beef to a plate and set aside.
03 - In the same pot, add onion, lemongrass, garlic, ginger, and red chilies. Sauté for 3-4 minutes until fragrant and onions are softened, stirring occasionally.
04 - Stir in fish sauce and brown sugar, cooking for 1 minute to dissolve sugar and meld flavors.
05 - Return beef and accumulated juices to the pot. Pour in coconut milk, beef broth, and add carrots. Bring mixture to a gentle simmer.
06 - Reduce heat to low, cover tightly, and braise for 1 hour. Maintain a gentle simmer throughout.
07 - Stir in quartered mushrooms. Cover and continue braising for another 1 to 1.5 hours until beef is fork-tender and sauce has thickened slightly.
08 - Discard lemongrass stalks. Stir in lime zest and juice. Taste and adjust seasoning with additional salt if needed.
09 - Ladle hot braised beef into bowls. Garnish generously with chopped cilantro, sliced scallions, and fresh lime wedges on the side.