Remove the outer leaves from the lemongrass stalks and reserve. Roughly chop the tender core and put into a food processor with the chillies, garlic, fresh ginger, onion, ground ginger, coriander, cumin, black pepper and 4 tablespoons of water. Blend to a smooth paste.
Heat the sunflower oil in a large flameproof casserole over a medium heat. Add the cinnamon sticks and cloves and allow them to sizzle for about 1 minute. Add the spice paste and bay leaves and fry gently for 2 minutes. Add the coconut milk, the beef, reserved lemongrass leaves and the salt and bring to the boil.
Meanwhile, if you are using the tamarind pulp, put in a small bowl with 120ml of warm water and work through with your fingers to release the seeds. Strain the syrupy mixture into a clean bowl and discard the seeds.
Lower the heat to a simmer, add the tamarind liquid and muscovado sugar and leave to cook uncovered for 21/2 hours, stirring more frequently as the liquid reduces, until the sauce is well reduced and quite thick and the beef is very tender. Garnish with the chilli and spring onion curls and serve with the fragrant rice and a cucumber, tomato, red onion and coriander salsa.