Heat oil in a large pot over medium heat and sauté onion until soft.

Add garlic, ginger, galangal, and chilies and cook until fragrant.

Stir in turmeric, coriander, cumin, and salt to toast the spices.

Add beef cubes and cook for several minutes until lightly browned.

Pour in coconut milk and water or broth and stir well.

Add lemongrass stalks and kaffir lime leaves.

Bring to a gentle simmer and cook on low heat for 1½ to 2 hours while stirring occasionally.

Stir in tamarind paste and brown sugar as the sauce thickens.

Continue cooking until the sauce becomes rich, dark, and thick.

Remove lemongrass and lime leaves and serve hot with rice.