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 until deeply browned on all sides, about 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. Sauté for 3-4 minutes until fragrant and onions are translucent, stirring occasionally to prevent burning.
04 - Stir in fish sauce and brown sugar. Cook for 1 minute, allowing the sugar to dissolve and the mixture to become aromatic.
05 - Return the seared beef and any accumulated juices to the pot. Add coconut milk, beef broth, and carrots. Bring the mixture to a gentle simmer, stirring to combine all ingredients.
06 - Reduce heat to low, cover tightly with a lid, and braise for 1 hour. Maintain a gentle simmer throughout—the liquid should barely bubble.
07 - Add quartered mushrooms and stir gently to incorporate. Cover again and continue braising for 1 to 1.5 hours, until beef is fork-tender and easily pulls apart.
08 - Remove and discard the lemongrass stalks. Stir in lime zest and fresh lime juice. Taste and adjust seasoning with additional salt or fish sauce if needed.
09 - Ladle the braised beef into bowls and serve hot, generously garnished with chopped fresh cilantro, sliced scallions, and additional lime wedges on the side.