Start by cutting the beef into medium-sized chunks and seasoning them lightly with salt and pepper. Slice the onions, mince the garlic, and prepare the lemongrass by bruising it to release its flavor. Having everything ready will make cooking smoother. This step sets the foundation for a well-balanced dish.

Heat oil in a large pot over medium-high heat and add the beef pieces in batches. Sear them until browned on all sides, which helps lock in juices and build flavor. Avoid overcrowding the pan to ensure proper browning. Once done, set the beef aside.

In the same pot, sauté onions and garlic until soft and fragrant. Add the lemongrass and cook for another minute to release its aroma. This step creates a rich, flavorful base that enhances the entire dish. Stir gently to prevent burning.

Pour in the coconut milk and beef broth, then stir in soy sauce, fish sauce, and brown sugar. Return the seared beef to the pot and bring everything to a gentle boil. Reduce the heat and let it simmer slowly. This allows the beef to become tender and absorb all the flavors.

After about an hour of simmering, add the sliced mushrooms to the pot. Stir well and continue cooking until the mushrooms are tender. They will absorb the sauce beautifully and add a meaty texture. This step enhances the overall richness of the dish.

Taste the dish and adjust salt and pepper as needed. Remove the lemongrass pieces before serving for a better eating experience. Garnish with fresh cilantro for a pop of freshness. Serve hot and enjoy the comforting flavors.