Heat oil in a Dutch oven over medium-high heat. Sear the beef in batches until each piece forms a golden crust. This step builds deep flavor that enhances the entire dish.
Lower the heat and add lemongrass, ginger, garlic, peppers, curry paste, lime leaves, and turmeric. Stir until fragrant and slightly softened, releasing all those rich and aromatic oils.
Add mushrooms and cook until they release moisture and brown slightly. Pour in coconut milk and water, then stir in sugar and fish sauce to create a rich, balanced sauce.
Return the beef to the pot along with onions and carrots. Cover and place it in the oven, allowing it to braise slowly until the beef becomes fork-tender and flavorful.
Remove from the oven and let it rest for about 30 minutes. This helps the flavors deepen and settle beautifully before serving with rice and garnishes.