Put the chillies, shallots, garlic, ginger, galangal and turmeric in a blender. Add 200ml of the measured coconut milk and blend, stopping to scrape down the sides, until no large pieces remain.
Scrape the paste into a wide, heavy pan. Add the remaining 600ml coconut milk, 300ml water, lemongrass, lime leaves, optional Indonesian bay leaves, optional turmeric leaf, tamarind paste, palm sugar and salt. Stir thoroughly and bring slowly to a gentle simmer over medium heat.
Add the beef and turn the pieces through the coconut mixture. Return to a gentle simmer, then reduce the heat. Keep the pan uncovered throughout cooking.
Simmer gently for about 1 hour, stirring and scraping the base every 15 minutes. The liquid should remain plentiful while changing from pale orange to golden brown. Do not let it boil vigorously.
Continue cooking for 45 to 60 minutes, stirring every 8 to 10 minutes, until the sauce is thick and brown. Test the beef. If it remains firm and the sauce is very thick, stir in 150ml hot water and continue simmering. Add the remaining hot water only if needed, allowing the first addition to reduce before deciding.
When the beef is nearly tender, turn the heat to low. Cook for 35 to 50 minutes more, stirring and scraping every 2 to 3 minutes at first and almost continuously near the end. Continue until the coconut oil separates and the solids form a deep brown coating around the meat.
Stop when the beef is fork tender and no watery sauce remains. Taste and add more salt if needed. Remove and discard the lemongrass and whole leaves.
Remove the pan from the heat and rest for 15 minutes. Turn the beef gently through the coating, then serve with rice and vegetables.