Trim lemongrass (1): reserve trimmings for the beef, finely chop the white part for the paste.
In a saucepan combine beef (700 g), beef broth (500 ml), bay leaves (2) and lemongrass trimmings (liquid should almost cover; top up with water). Boil, then simmer gently 1.5–2 hours until fork tender. Remove beef; reduce liquid to about 375ml and reserve.
In a dry, smoking-hot skillet char shallots (4), garlic (5) and galangal (1) ~1.5 min; remove. Char dried chillies (6) 10 sec each side. Cool, then grate galangal, peel garlic, and deseed chillies.
In a clean skillet over medium, toast cloves (1/2 tsp), cumin (3/4 tsp), nutmeg (1/8 tsp), coriander (3/4 tsp), cardamom (1/2 tsp) and cinnamon (1/2 tsp) 30 sec until fragrant; don't burn.
Blitz chillies in a processor, then add galangal, chopped lemongrass, toasted spices, shallots and garlic with 4 tbsp water (90 ml); blend smooth, adding water as needed.
Heat oil (65 ml) over medium-high; fry paste 3 min until thick and fragrant. Stir in coconut milk (400 ml), then add cinnamon quill (1), star anise (1) and reserved braising liquid; simmer 3 min on medium. Stir in fish sauce (1 tbsp), tamarind (1 tsp), sugar (1 tbsp). Add potatoes (2), cook 7 min until tender, then add beef (700 g) and simmer 2 min until thickened. Adjust sweet/salty/sour to taste; thin with water if needed.
Serve over jasmine rice topped with chopped peanuts (3 tbsp), fried shallots and sliced chilli.